Description

These Buttery Roast Beef Sliders with Caramelized Onions are delightfully rich and packed with layers of savory flavors. Featuring slow-cooked sweet onions, melty cheeses, and a luscious garlic butter topping, all nestled between soft slider buns. Served with a warm au jus sauce perfect for dipping, these sliders make a perfect crowd-pleasing appetizer or main dish for parties and family gatherings.

Ingredients

Scale

For the Caramelized Onions

2 tablespoons unsalted butter
1 tablespoon olive oil
3 large yellow onions, thinly sliced
½ teaspoon kosher salt
1 teaspoon brown sugar, optional, helps speed up caramelization
2 tablespoons beef broth, for deglazing

For the Homemade Garlic Aioli

1 large egg yolk, room temperature
1 teaspoon Dijon mustard
1 garlic clove, finely grated or minced
1 tablespoon fresh lemon juice
½ cup light olive oil or neutral oil
Kosher salt, to taste

For the Au Jus Sauce

¼ cup unsalted butter
1 tablespoon Better than Bouillon Beef Base
2 cups beef broth
2 teaspoons Worcestershire sauce

For the Roast Beef Sliders

12 slider buns, sliced in half (Hawaiian rolls preferred)
¼ cup homemade garlic aioli or mayonnaise
½ pound deli roast beef, thinly sliced
12 slices melty cheese (like provolone, Swiss, or muenster)
½ cup shredded mozzarella cheese
2 cups caramelized onions

For the Garlic Butter Sauce

6 tablespoons unsalted butter, melted
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
Freshly cracked black pepper, to taste

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Instructions

Make the Caramelized Onions: Melt the butter and olive oil in a large skillet over medium-low heat. Add the thinly sliced onions, sprinkle in the kosher salt and brown sugar (if using), and cook gently, stirring occasionally, until the onions become soft, deeply golden, and jammy, about 45 minutes. Towards the end, stir in the beef broth to deglaze the pan and lift all the caramelized bits. Remove from heat and set aside.
Make the Garlic Aioli: In a small bowl, whisk together the egg yolk, Dijon mustard, grated garlic, and lemon juice until smooth. While continuing to whisk or blending with an immersion blender, slowly drizzle in the light olive oil or neutral oil until the mixture thickens into a creamy aioli. Season with kosher salt to taste and set aside. For a shortcut, use mayonnaise mixed with garlic, mustard, lemon, and salt.
Prepare the Au Jus Sauce: Melt the butter in a medium saucepan over medium heat. Stir in the Better than Bouillon Beef Base, beef broth, and Worcestershire sauce. Allow the sauce to simmer gently for 20 minutes until it reduces by about half, darkening slightly and thickening a bit as it cools. Keep warm until serving.
Toast the Bottom Buns: Preheat the oven to 350°F (180°C or Gas Mark 5). Slice the slider buns in half horizontally without separating them. Place the bottom halves on a parchment-lined baking sheet, brush lightly with melted butter or aioli, and toast in the oven for 5 minutes until just golden.
Assemble the Sliders: Spread a generous layer of garlic aioli over the toasted bottom buns. Pile the thinly sliced roast beef evenly on top, layering 2–3 slices for hearty sliders. Place one slice of melty cheese on each slider, then sprinkle the shredded mozzarella evenly over the tops. Spoon a layer of caramelized onions over the cheese.
Add the Tops and Bake: Place the top halves of the buns on the sliders. In a small bowl, mix melted butter, Worcestershire sauce, poppy seeds, white sesame seeds, garlic powder, dried minced onion, kosher salt, and freshly cracked black pepper. Brush this garlic butter mixture generously over the tops of the buns. Cover the sliders loosely with foil and bake for 10 minutes. Remove the foil and bake for an additional 10 minutes until the tops are golden brown and the cheese has melted beautifully.
Serve: Slice between the rolls to separate the sliders. Serve warm immediately with small bowls of the warm au jus sauce for dipping. Enjoy!

Notes

For a quicker version, skip caramelizing the onions and use seasoned mayo mixed with garlic and lemon for the aioli. This reduces prep time to about 30 minutes.
Make sliders up to two days ahead without caramelized onions and garlic butter. Add these just before baking for freshest flavor.
Store leftover sliders in an airtight container for up to 3 days.
Reheat leftover sliders in the oven at 375°F for about 10 minutes to avoid sogginess.
Use Hawaiian rolls for the best soft texture, but any slider buns will work.
If avoiding raw egg yolk, substitute the aioli with high-quality mayonnaise mixed with garlic, mustard, and lemon.

Nutrition

Serving Size: 1 slider
Calories: 280 kcal
Sugar: 3 g
Sodium: 450 mg
Fat: 16 g
Saturated Fat: 7 g
Unsaturated Fat: 7 g
Trans Fat: 0 g
Carbohydrates: 18 g
Fiber: 1 g
Protein: 14 g
Cholesterol: 50 mg