01 -
Heat the oven according to the Texas toast package directions. Arrange the slices on a sheet pan and bake until golden and crisp, usually 8-10 minutes.
02 -
In a small saucepan, whisk together beef broth, water, Worcestershire sauce, onion powder, garlic powder, and black pepper. Simmer for 4-5 minutes, then whisk in the butter.
03 -
Reduce the heat to low. Add the sliced roast beef to the hot au jus for 1-2 minutes, just until warmed through. Lift the beef out with tongs and keep the jus hot for serving.
04 -
Spread horseradish on 4 toast slices if using. Divide the warm roast beef over those slices and top each one with 2 slices of provolone.
05 -
Return the topped toast to the oven or place under the broiler for 1-3 minutes, just until the cheese melts. Watch closely so the toast does not burn.
06 -
Top with the remaining Texas toast slices, sprinkle with parsley, and serve immediately with small bowls of hot au jus for dipping.