As soon as my mom tasted it, she rushed over to get the recipe from me.

1 lb ground beef
1 large onion, thinly sliced
8 slices rye bread
4 slices Swiss cheese
4 slices cheddar cheese
Butter, for grilling
Salt and pepper, to taste
1/2 cup mayonnaise
2 tablespoons ketchup
1 tablespoon sweet pickle relish
1 teaspoon Worcestershire sauce