Preheat the oven to 400° F.
Combine the butter, au jus, Worcestershire, garlic powder, and onion powder.
Cut an odd number of slices into your loaf of bread. Do not cut the bread all of the way through, only about ¾ quarter of the way through. It should remind you of an accordian when you're done.
Spread the butter mixture on all of the slices that you cut.
Place one or two slices of provolone and one or two slices of roast beef in every other slit of bread. When you pull it apart, each serving will need 2 slices of bread as a sandwich. If this is confusing, just mimic the picture of the recipe.
If you have any butter left, spread it on top of the sandwich.
Wrap the sandwich in tin foil.
Bake for 10 minutes.