This is a great sandwich for the Fourth of July when you have a few friends over and you can watch their eyes pop out!
Preheat the oven to 400 degrees F (200 degrees C).
Slice the loaf of French bread HORIZONTALLY into 5 equal layers. Spread bottom layer with horseradish, top with roast beef. Place the next slice of bread over beef, spread with mustard and top with ham and Swiss cheese. Add next slice of bread, spread with mayonnaise and top with turkey and cheese. Add the next slice of bread, spread with more mayonnaise top with tomato and onion. Cover with top. Brush melted butter over top and sides of loaf (if desired). Place on a baking sheet, loosely tent with heavy duty foil.
Bake for 15 to 20 minutes in the preheated oven, or until cheese is melted and sandwich is heated through. Carefully slice into 6 slices and serve.
Per Serving: 710 calories; protein 46.8g; carbohydrates 47.2g; fat 37g; cholesterol 134.2mg; sodium 1933.6mg.