Preheat oven to 350°F (175°C). Grease a 9×13-inch baking pan with 2 tablespoons of butter and line with parchment paper.

Slice the block of rolls horizontally, keeping them attached, and place the bottom half in the pan.

Assemble the Sliders:

Layer 6 slices of cheese, roast beef, optional fried onions, remaining 6 cheese slices, then top with the other half of the rolls.

Make the Butter Topping:

In a small microwave-safe bowl, melt 8 tablespoons butter. Add 1 tablespoon of au jus mix, Worcestershire sauce, sesame seeds, garlic, and onion powder. Whisk to combine.

Spread the mixture evenly over the top and sides of the rolls. Reserve leftover butter mixture for future use.

Bake:

Bake uncovered for 15–20 minutes until cheese is melted and tops of rolls are golden brown.

Prepare Au Jus:

Heat remaining au jus mix with water in a small saucepan over medium heat. Bring to a boil, then simmer until slightly thickened.

Serve:

Cut sliders along the roll divisions and serve warm with au jus for dipping.