So much beef, you can't say no.
To make the au jus, melt the reserved drippings from roast beef in a skillet. Add flour and whisk until thickened. Add broth, red wine, green onions, and garlic powder to skillet and stir. Simmer until slightly thickened, about ten minutes. Add salt and pepper to taste. Reserve.
Preheat the oven to 375 F (190 C).
Cut the baguettes in half. Brush the cut sides with butter, and sprinkle with garlic salt. Bake in the oven for six to eight minutes or until golden brown. Remove from oven and spread with mayonnaise and horseradish.
Place a few slices of roast beef on each bottom piece of bread. Place a slice of cheese on each top piece of bread. Place back in the oven for four to six minutes, or until the cheese melts. Remove from oven and assemble. Cut sandwiches into pieces about 15-20 centimeters wide. Serve immediately with a side of au jus for dipping.