Soak oats in boiling water for 20 minutes. Meanwhile, cream butter and white and brown sugars until smooth. Add eggs and beat. Add soaked oats and mix well. Add dry ingredients and mix well. Bake in a greased 9x1 3x2" pan at 375° for 25 minutes. (Cake is done when knife inserted in center comes out clean.)
Combine frosting ingredients one at a time in the order given. Spread evenly on cooled cake.