Banana Cake

2/3 cup shortening
1 1/2 cups granulated sugar
2 eggs, separated
4 tablespoons sour milk*
1 teaspoon baking soda
2 cups all-purpose flour
1 teaspoon vanilla extract
1 cup bananas, mashed

* To make milk sour, add 1 teaspoon vinegar.

Cream shortening and sugar. Add egg yolks. Combine sour milk and baking soda and set aside. Add flour to sugar-shortening mixture. Add milk mixture. Stir. Add vanilla extract and bananas. Beat egg whites and fold into mixture. Bake in well-greased 9-inch square baking dish for about 45 minutes at 350 degrees F.