To make Frisco sauce, you need 4 tablespoons of mayonnaise, 1 1/3 tablespoons of ketchup, 1 teaspoon of granulated sugar and 1/2 teaspoon of pickle relish. Mix all the ingredients together in a bowl to create Frisco sauce.
Copycat Frisco melts from Stake 'n' Shake are made by taking 1 pound of ground beef or chuck and splitting it into eight different patties, then frying them. Assemble 8 slices of bread, and lightly toast them all. Drain all the excess fat from the skillet or pan, and add 1/2 tablespoon of butter or margarine at medium heat. Add onions once the butter or margarine has melted. Allow the onions to cook until they are softened, and then remove them from the skillet without draining.
Place as many slices of bread in the skillet as possible, and cook both sides of the bread for one to two minutes. Remove the bread from the skillet, and top half of the slices with one slice of American cheese and one beef patty. Add a slice of Swiss cheese on top of the patty, and then place another beef patty on top of the Swiss cheese. Place one more slice of American cheese on top of the second patty, and then add the onions. Spread the Frisco sauce on the remaining slices of bread, and then place those slices on top of the sandwiches to complete them.