01 -
Cut the rolls in half across the middle.
02 -
Place the rolls under the broiler for a minute or two, until lightly browned.
03 -
Set the oven temperature to 350 degrees Fahrenheit.
04 -
Blend together the mayonnaise and horseradish until smooth.
05 -
In a baking dish, stack the bottom rolls, a layer of mayo mix, half the cheese, roast beef slices, caramelized onions, more cheese, and finally the top rolls spread with mayo.
06 -
Combine the butter sauce ingredients and coat the tops and edges of the rolls with it using a brush.
07 -
Cover the dish and bake for 20 minutes. Remove the covering, and continue baking for another 5-8 minutes.
08 -
In a pan, heat the butter and cook chopped garlic just until it smells fragrant. Stir in flour if you want a thicker result, and cook for a minute or two.
09 -
Stir the stock, Worcestershire, seasoning, and optional beef base into the pan. Let it simmer for about 10 minutes.
10 -
Run the sauce through a strainer and serve it warm as a dip for the sliders.