Ingredients
1/4 cup mayonnaise
1/4 cup spicy mustard
3 to 4 tablespoons poppy seeds
3 tablespoons grated onion
1 tablespoon horseradish mayonnaise
12 soft hamburger buns, sliced in half
1 pound thinly shaved roast beef
8 ounces sliced provolone
8 ounces American cheese