Beat together 1/2 cup sugar, 1/2 cup butter, 1 egg and 1 cup molasses. Sift together 2 cups flour, 1 tablespoon ginger, 1 teaspoon cinnamon, and 1/2 teaspoon salt. Mix 1 cup sour milk with 1 teaspoon baking soda. Alternate adding flour and milk mixture to molasses mixture, beginning and ending with flour mixture for a lighter cake. Mix thoroughly. Pour into a greased 9×13″ pan. Bake at 350 for 30 minutes or until done.