There’s something truly irresistible about a soft bun filled with tender roast beef, melty cheese, and those sweet, slow-cooked onions. This Buttery Roast Beef Sliders with Caramelized Onions Recipe is my go-to when I want to impress guests or just treat myself to a seriously delicious slider experience.

Two toasted sandwich buns with a golden brown color and sprinkled with sesame seeds and seasoning sit stacked on a dark wooden board. The bottom bun holds a layer of melted cheese that drapes over the edges, topped with caramelized onions and slices of cooked meat peeking out from under the cheese. The top bun rests slightly off-center on the filling, showing more melted cheese and caramelized onions oozing from the sides. The background is dark, and the board contrasts with the textures of soft buns, shiny melted cheese, and juicy meat and onions. Photo taken with an iphone --ar 2:3 --v 7

Jump to:

Why You'll Love This Recipe
Ingredients & Why They Work
Make It Your Way
Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe
Top Tip
How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe
Make Ahead and Storage
Frequently Asked Questions:
Final Thoughts
Buttery Roast Beef Sliders with Caramelized Onions Recipe

Why You'll Love This Recipe

I can’t tell you how many times these roast beef sliders have saved the day, whether for game day, a quick family dinner, or when friends just drop by unexpectedly. They’re simple to make but look and taste like you put in way more effort than you really did.

Flavor-packed Layers: Caramelized onions bring that sweet, savory depth that pairs perfectly with juicy roast beef.
Homemade Touch: The garlic aioli and au jus sauce add richness and a touch of gourmet flair.
Perfect for Entertaining: Sliders are always a crowd favorite and easy for guests to grab and enjoy.
Soft & Buttery Buns: Using Hawaiian rolls makes these sliders irresistibly soft and slightly sweet, balancing out the savory filling.

Ingredients & Why They Work

Before you start, it’s worth grabbing some quality ingredients to get the best flavor. I like to scout for fresh yellow onions for the caramelizing process and lean deli roast beef that’s thinly sliced so it layers beautifully in the buns without overwhelming every bite.

Flat lay of a stack of 3 large yellow onions, thinly sliced; a small white ceramic bowl with a smooth pale yellow egg yolk; a single whole garlic clove, white and firm; a small white ceramic bowl filled with light golden olive oil; a small white ceramic bowl with bright yellow fresh lemon juice; a pat of unsalted butter, pale creamy and rectangular; a small white ceramic bowl of brown sugar; a small white ceramic bowl of coarse kosher salt; a small white ceramic bowl of deep brown beef broth; a small white ceramic bowl of dark Worcestershire sauce; a handful of thinly sliced deli roast beef, deep red with marbled fat; twelve soft, round slider buns with a glossy golden-brown crust sliced in half; twelve smooth, pale provolone cheese slices; a small white ceramic bowl of shredded white mozzarella cheese; a small white ceramic bowl with poppy seeds; a small white ceramic bowl with white sesame seeds; a small white ceramic bowl with dried minced onion; a small white ceramic bowl with garlic powder; a few whole brown eggs with clean shells arranged symmetrically nearby, placed on a clean white marble surface, soft natural light, photo taken with an iPhone, professional food photography style, fresh ingredients, white ceramic bowls, no bottles, no duplicates, no utensils, no packaging --ar 2:3 --v 7 --p m7354615311229779997

Unsalted Butter: Essential for controlling the richness and balancing the flavors in the onions, garlic butter sauce, and au jus.
Olive Oil: Adds a subtle fruitiness when cooking the onions and helps the caramelization process.
Yellow Onions: Their natural sweetness deepens as they cook low and slow into caramelized perfection.
Kosher Salt: Draws out moisture and enhances all the flavors without being overpowering.
Brown Sugar: Speeds up caramelization and adds a gentle sweetness to the onions.
Beef Broth: Used both in the onions and au jus for an authentic savory depth.
Egg Yolk: The heart of the homemade garlic aioli, giving it that creamy, luscious texture.
Dijon Mustard: Adds a subtle tanginess to the aioli, complementing the beef beautifully.
Garlic: Freshly grated for a bright punch of flavor in the aioli and butter sauce.
Fresh Lemon Juice: Balances the richness of the aioli with a fresh citrus note.
Light Olive Oil or Neutral Oil: Used to emulsify the aioli without overpowering the garlic.
Better than Bouillon Beef Base: An easy way to boost the flavor of your au jus with intense beefy richness.
Worcestershire Sauce: Adds a savory umami kick to both the au jus and garlic butter topping.
Slider Buns (Hawaiian Rolls preferred): Soft, slightly sweet, and perfect for layering all those juicy ingredients.
Deli Roast Beef: Thinly sliced for easy layering and maximum tenderness.
Melty Cheese (Provolone, Swiss, or Muenster): These cheeses melt beautifully and marry well with beef and onions.
Shredded Mozzarella Cheese: Adds extra gooeyness and meltiness to every bite.
Poppy Seeds & White Sesame Seeds: Bring a delightful crunch and nutty aroma to the garlic butter sauce.
Garlic Powder & Dried Minced Onion: Enhance the butter topping with savory depth and aroma.
Freshly Cracked Black Pepper: A finishing touch for complexity and a bit of heat.

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Note: You'll find the complete list of ingredients, along with their exact measurements, in the printable recipe card at the bottom of this post.

Make It Your Way

One of the best things about this Buttery Roast Beef Sliders with Caramelized Onions Recipe is how easy it is to customize to your taste or occasion. Whether you want to tweak the toppings, swap cheeses, or cater to dietary preferences, there’s plenty of room to make these sliders uniquely yours.

Cheese Swaps: I love using provolone for its mild meltiness, but Swiss or muenster add a wonderful nutty or creamy flair. Feel free to mix and match for a cheese lover’s dream.
Make it Spicy: For a little kick, add a dash of hot sauce to your aioli or sprinkle some crushed red pepper flakes into the caramelized onions. I tried this once and the subtle heat really brought the savory flavors to life.
Vegetarian Version: Swap the roast beef with grilled portobello mushrooms or your favorite plant-based deli slices, and keep all the other layers intact. The caramelized onions and garlic aioli bring so much flavor, you won’t miss the meat!
Quick Fix: If you’re short on time, skip caramelizing onions and spread mayo mixed with a little garlic and lemon to keep it easy but still packed with flavor.
Seasonal Twist: Add a layer of roasted red peppers or sautéed mushrooms during fall for a cozy, seasonal slider variation.

Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe

A close-up shows a woman's hand holding a sandwich with three layers: a toasted, sesame and poppy seed covered top bun in golden brown with a shiny glaze; inside there are layers of caramelized onions in dark brown with a glossy texture, melted cheese dripping in light yellow, and thin slices of cooked meat in pink with browned edges; below is the bottom bun matching the top in texture and color. The sandwich is being dipped into a white bowl filled with thick, brown dipping sauce that is dripping down the sides and splashing on the wooden surface below. In the background, there are more stacked sandwiches with the same layers on a wooden board, set against a white marbled textured surface. Photo taken with an iphone --ar 2:3 --v 7

Step 1: Slowly Caramelize Those Onions

Start by melting 2 tablespoons of unsalted butter with 1 tablespoon olive oil in a large skillet over medium-low heat. Add 3 large thinly sliced yellow onions, then sprinkle in ½ teaspoon kosher salt and 1 teaspoon brown sugar. Patience is key here—cook the onions slowly for about 35–45 minutes, stirring occasionally. You’ll know they’re done when they’re deeply golden brown, soft, and as sweet and jammy as candy. Finish by stirring in 2 tablespoons beef broth to deglaze the pan and scoop up all the tasty browned bits. Set your caramelized onions aside and get ready for the next step!

Step 2: Whip Up That Creamy Garlic Aioli

In a small bowl, whisk together 1 large room temperature egg yolk, 1 teaspoon Dijon mustard, the finely grated clove of garlic, and 1 tablespoon fresh lemon juice until smooth. Slowly drizzle in ½ cup light olive or neutral oil while whisking vigorously, or use an immersion blender to emulsify until the mixture thickens into a creamy aioli. Don’t forget to season with a pinch of kosher salt! If you prefer an easier method, simply mix these ingredients into mayonnaise—equally delicious and ready in minutes.

Step 3: Simmer the Savory Au Jus Sauce

Melt ¼ cup unsalted butter in a medium saucepan over medium heat. Stir in 1 tablespoon Better than Bouillon Beef Base, 2 cups beef broth, and 2 teaspoons Worcestershire sauce. Let the sauce simmer gently for 15–20 minutes until reduced by half. It will darken and thicken a bit as it cools—perfect for dipping your sliders into a savory bath of flavor. Keep it warm until serving.

Step 4: Toast the Bottom Slider Buns

Preheat your oven to 350°F (180°C). Slice 12 slider buns in half horizontally but keep the halves together so you can toast the bottoms on a parchment-lined baking sheet. Brush the cut sides lightly with melted butter or some of your homemade garlic aioli for irresistible flavor. Toast them in the oven for about 5 minutes until they’re just lightly golden and ready to hold all the delicious fillings without becoming soggy.

Step 5: Layer Up the Sliders Like a Pro

Spread a generous layer of garlic aioli over the toasted bottom buns. Next, pile on thinly sliced roast beef—about ½ pound divided evenly to build 2 to 3 hearty layers that’ll make every bite full and satisfying. Top the beef with 12 slices of your chosen melty cheese, then sprinkle on ½ cup shredded mozzarella for extra gooey goodness. Finally, spoon an even layer of those glorious caramelized onions right on top. Each ingredient adds its own magic, so don’t be shy!

Step 6: Butter, Bake, and Bring It All Together

Place the top halves of the buns on your stacked sliders. In a small bowl, mix 6 tablespoons melted unsalted butter with 1 teaspoon Worcestershire sauce, 1 tablespoon poppy seeds, 1 tablespoon white sesame seeds, ½ tablespoon garlic powder, ½ tablespoon dried minced onion, ½ teaspoon kosher salt, and freshly cracked black pepper to taste. Brush this flavorful garlic butter sauce generously over the tops. Cover loosely with foil and bake in the oven for 10 minutes. Remove the foil and bake for an additional 5 to 10 minutes until the tops turn a beautiful golden brown and the cheese is delectably melted.

Step 7: Slice, Serve, and Dip Away!

Once out of the oven, carefully slice between the rolls to separate your sliders. Serve them warm alongside individual bowls of the luscious au jus sauce for that classic dipping experience. Trust me, these warm, buttery, cheesy sliders with sweet caramelized onions and garlic aioli will have everyone coming back for seconds—and thirds!

Top Tip

To get the most out of your Buttery Roast Beef Sliders with Caramelized Onions Recipe, these tips will help make your sliders irresistibly flavorful and perfectly textured every time.

Low and Slow Caramelization: Be patient with your onions—cooking them on medium-low heat for 35–45 minutes creates that perfect jammy sweetness that truly elevates these sliders.
Garlic Aioli Magic: Whisk the aioli ingredients slowly and steadily, adding the oil drop-by-drop to get a creamy, stable emulsion which adds a rich, garlicky punch without overpowering the roast beef.
Butter Brush Boost: Don’t skimp on brushing the tops generously with the garlic butter mixture before baking; it adds beautiful color, incredible flavor, and that delightful crunch on top.
Don’t Skip Toasting the Bottom Buns: Toasting the bottom buns before assembling keeps them from getting soggy and adds a lovely buttery crisp base for all your delicious layers.

How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe

The image shows five pieces of bread spread with a creamy white mixture that has small green flecks, all placed neatly in a baking tray. The bread pieces vary in size and shape, with three longer slices arranged horizontally on the top and middle, and two smaller slices on the lower right side. The creamy spread is unevenly applied, with some areas thicker and others thinner, showing a rough texture on the bread underneath. The baking tray has a light beige tone, and the background surface has been changed to a white marbled texture. Photo taken with an iphone --ar 2:3 --v 7

Garnishes

For a little extra pop and festive flair, you can add some fresh herbs like chopped parsley or chives on top right after baking. A few crunchy dill pickle slices or thinly sliced pickled jalapeños on the side bring brightness that cuts through the buttery richness. And if you like, serve with little ramekins of whole grain mustard or horseradish sauce for dipping alongside the au jus for extra zing.

Side Dishes

Roast beef sliders love good sides! Try crispy oven-baked sweet potato fries, classic kettle potato chips, or a light crisp coleslaw for a refreshing crunch. A simple green salad with a tangy vinaigrette or roasted garlic parmesan asparagus also pairs beautifully to balance this hearty, melty slider experience.

Make Ahead and Storage

Storing Leftovers

After enjoying your sliders, simply store any leftovers sealed airtight in the refrigerator. They will keep well for up to 3 days and stay fresh enough to enjoy again without losing their signature buttery flavor and tender texture.

Freezing

While the sliders are best fresh, you can freeze assembled sliders (without baking) wrapped tightly in plastic wrap and foil, then placed in a freezer-safe container for up to one month. When ready, thaw overnight in the fridge and bake as instructed, adding fresh caramelized onions and garlic butter before baking.

Reheating

To enjoy leftovers, reheat in a preheated oven at 375°F for about 10 minutes. This method keeps the buns from getting soggy and ensures your cheese melts perfectly all over again. Avoid microwaving as it can make the buns chewy and dry out the meat.

Frequently Asked Questions:

Can I make the caramelized onions ahead of time?

Absolutely! Caramelized onions can be prepared up to 3 days ahead and refrigerated in an airtight container. Reheat gently before assembling the sliders for the best flavor and texture.

Is it safe to use raw egg yolk in the garlic aioli?

Yes, but make sure to use fresh, high-quality eggs from a trusted source. Alternatively, you can use mayonnaise as a shortcut to make a delicious garlic aioli if you prefer to avoid raw egg.

What cheese works best for these sliders?

Provolone, Swiss, and muenster are all wonderful choices for meltability and mild flavor that complements the roast beef. Adding shredded mozzarella on top ensures an extra gooey, melty finish.

Can I use sandwich rolls other than Hawaiian buns?

You can, but Hawaiian rolls are preferred for their soft texture and subtle sweetness, which balances the savory and buttery notes beautifully. If you use other rolls, aim for ones that are soft and slightly sweet.

Final Thoughts

Making these Buttery Roast Beef Sliders with Caramelized Onions always feels like a little celebration in my kitchen. The way those softened onions meld with the tender roast beef, oozing melty cheese, and that garlicky buttered bun creates a harmony that’s hard to beat. Whether it’s for game day, a cozy dinner, or impressing guests, these sliders deliver comfort and flavor in every bite. I hope this recipe becomes a favorite in your home as it is in mine—happy cooking and even happier eating!