Preheat oven to 400 degree F. Grease 9-inch square baking pan; set aside. In medium pan, combine soup, eggs, and milk. Stir in corn muffin mix just until blended. Gently fold in sausage. Spoon corn muffin mixture into prepared pan, spreading evenly. Bake 20 minutes or until lightly browned and toothpick inserted in middle comes out clean. Cool on wire rack 10 minutes before cutting into squares.
Brown beef and onion in oil in 10-inch skillet until onion transparent. Add soup, mushrooms, and water; simmer covered 20 minutes. Add sour cream and heat 5 more minutes. Serve over hot noodles.