Cream 1 cup sugar and butter. Add egg yolks and sour cream. Beat until light and fluffy. Add flour, baking powder and baking soda. Beat egg whites until stiff and fold in. Pour batter into a greased and floured Bundt pan.
Sprinkle with topping made of quarter c sugar, cinnamon and nuts. Dot with extra butter. Bake at 160ºC or 1 hour. Allow to cool in pan for 15 minutes before turning out.