Cut Bread Horizontally Into Six Slices. Spread Bottom Slice With Horseradish; Top With Roast Beef. Place The Next Slice Of Bread Over Beef; Spread With Mayonnaise And Top With Swiss Cheese. Add Next Slice Of Bread; Spread With Mustard And Top With Ham. Add The Next Slice Of Bread; Top With Bacon And American Cheese. Add Next Slice Of Bread; Top With Tomato And Onion. Spread Butter On Cut Side Of Bread Top; Cover Sandwich. Place On A Baking Sheet; Loosely Tent With Heavy-Duty Foil. Bake At 400 Degrees F For 12-14 Minutes Or Until Heated Through. Carefully Slice Into Wedges