blueberries, or whatever berry you prefer
Beat butter and sugar until creamy. Add beaten egg yolk. Sift flour and baking powder. Add milk and sifted dry ingredients alternately. Stir in vanilla, then blueberries.
Beat eggs whites until stiff. Gently fold in egg whites.
Spread in a prepared loaf pan. Bake at 375 until cake tests done. Depends on size of pan, usually around 30-40 mins.
Cool slightly and remove cake from pan. Brush with butter and sprinkle with a little sugar. This is so good sliced and toasted and made into french toast.