PREP: Generously grease a 9x13-inch pan with cooking spray and line with parchment paper. Preheat oven to 350 degrees F. Slice the slab of rolls in half horizontally, keeping individual rolls intact.
SAUCE: Whisk mayo and horey sauce together. Spread mixture evenly across the inside surfaces of both the base and the top of the rolls.
ASSEMBLE: Place the base slab in the pan and top with 6 slices of cheese. Add roast beef on top then add the remaining 6 slices of cheese on top of the veggies.
BAKE: Bake WITHOUT the top for 10 minutes, to let the cheese melt. Meanwhile, combine all “butter” ingredients and briskly whisk until smooth.
ADD BUTTER: Remove pan from oven and add the top slab of rolls. Pour the butter all over, brushing generously on top and on the sides of the rolls. Be sure to cover all the bread (except the bottoms). (It's fine if you don't use it all or some of the butter pools at the bottom -- it will make the base crispy!)
BAKE AGAIN: Cover with foil and bake for 20 minutes. Remove foil and bake another 5-10 minutes or until golden brown on top and cheese is melty.
ENJOY: Cut and serve while hot. Enjoy!
Video
Notes
Note 1: Rolls: Keep the rolls intact and slice them in half horizontally so they open like a book.Note 2: The horsey sauce adds a unique, tangy flavor. Grab Arby's horsey sauce from your local Arby's or grocery store. If you can't find it, don't worry, these sliders are still tasty without it!Note 3: For the juiciest sliders, ask for the rarest roast beef from the deli counter to ensure it stays tender and doesn't overcook during baking. For less meaty sliders, use 3/4 pound of roast beef; for meatier sliders, use 1 pound.