Place all dry ingredients of the cake into mixing bowl. Add liquids and mix well. Prepare 9 X 13 pan and pour batter into the pan. Bake at 350 degrees for 30 minutes.(If at high altitude add 1/4 cup flour to this batter).
After cake cools mix peanutbutter, margarine or butter together and then add powdered sugar. Add milk very slowly until good spreading consistency is reached. Frost the cooled cake.