Banana Sheet Cake
["2 sticks butter", "1/2 c. water", "2 c. sugar", "2 c. flour", "1/2 tsp. soda", "1/4 c. sour milk", "1 c. mashed banana", "walnuts (optional)"]
["Bring first 2 ingredients to a boil.", "Add remaining ingredients.", "Bake at 350\u00b0 for 20 minutes; cool before frosting."]
["butter", "water", "sugar", "flour", "soda", "sour milk", "banana", "walnuts"]