Mix sifted flour, sugar and margarine until crumbly. Set aside 1/2 c. To the remaining crumb mixture add remaining ingredients as given above. Beat well with mixer on low speed. Spread evenly in a greased 8" square pan. Unrinkle reserved crumbs over top and bake at 350~ for 35 to 40 minutes or until inserted toothpick comes out clean. Dust warm cake with powdered sugar before cutting.