Layered Tostada Bake

A quick Mexican-inspired meal that's all-in-one.

Ingredients
1 lb. extra lean ground beef
1 medium onion, chopped
1/2 C. taco seasoning mix
8 oz. can tomato sauce
1 16 oz. can nonfat refried beans
1 C. reduced fat Bisquick
1/2 C. cornmeal
1/4 C. skim milk, at room temperature
1 egg white
2 Tbs. olive oil
1 C. nonfat sour cream
1 egg white
2 C. nonfat cheddar cheese, shredded

Directions
Preheat oven at 375 degrees. Prepare a 12x7x2" baking dish, with cooking spray. Cook and stir beef and onion in a skillet until meat is brown. Stir in seasoning mix, tomato sauce and beans. In a mixing bowl, combine baking mix, cornmeal, milk, egg white, and oil until moistened. Spread in dish. Spoon meat mixture over dough. Mix remaining ingredients; spoon over meat mixture. Bake uncovered 30 minutes. Let stand