Mix sifted flour, sugar and margarine until crumbly.
Set aside half c. To the remaining crumb mixture add remaining ingredients as given above. Beat well with mixer on low speed. Spread evenly in a greased 20 cm square pan. unrinkle reserved crumbs over top and bake at 180ºC for 35 to 40 minutes or until inserted toothpick comes out clean. Dust warm cake with powdered sugar before cutting.