Impossibly Easy Cheeseburger Pie

1 lb ground beef
1 lg onion, chopped
1/2 tsp salt
1 C shredded cheddar cheese
1/2 C Bisquick
1 C milk
2 eggs

Heat oven to 400. Grease 9" pie plate. Cook beef & onion until beef is brown; drain. Spread in pie plate, sprinkle with cheese. Stir remaining ingredients until blended. Pour into pie plate. Bake 25 minutes. Cool 5 minutes. Done when knife inserted in the center comes out clean.