Preheat oven to 400. Can be topped with crisply cooked bacon. Grease pie plate, 10x1 1/2", or sq. Baking dish, 8x8, or 6 10 oz. Custard cups. Cook and stir gr. Beef and onion in 10" skillet over med. Heat until beef is brown; drain. Stir in salt and pepper.
Spread in pie plate. Beat milk, eggs and baking mix 15 sec. In blender on high speed, 1 min. With wire whisk or hand beater or until smooth. Pour into pie plate. Bake 30 min. Top with tomato slices; sprinkle with cheese. Bake 5-8 min. Or til knife comes out clean. Cool 5 min. 1/2 Recipe: Use 1 qt. Square or round casserole. Decrease eggs to 2 and baking mix to 1/2 c. Divide remaining ingred. Amts. In half.
Decrease beat time to 10 sec. In blender or 30 sec. With wire whisk or hand beater. High Alt>Increase first bake to 30 min. If baking the 1/2 recipe: Use 1 1/2 qt round casserole or 1 qt. Square.