Preheat oven to 350. Brown the meat, drain, and set aside. In a 8" round pan, place 1 tortilla in the bottom. Top with 1/4 cup ground beef, cover with cheese, then taco sauce. Repeat layers twice. Place remaining tortilla shell on top, cover with cheese and taco sauce. Bake for 20 minutes or until hot and bubbly. Serve with tomatoes, sour cream, additional taco sauce, or any other toppings you prefer.