Easy Banana Sheet Cake
["2 large ripe bananas, mashed well or 3 small ripe bananas", "1 1/2 sticks margarine", "1/2 c. water", "2 c. flour", "1/2 tsp. salt", "1/2 tsp. soda", "1/2 c. sour milk"]
["To sour milk, add 1 tablespoon vinegar or lemon juice to milk to equal 1/2 cup.", "Let stand until it curdles."]
["bananas", "margarine", "water", "flour", "salt", "soda", "sour milk"]