In a mixing bowl, beat egg and half cup sugar. Combine flour, baking powder, and salt; add alternately with milk to sugar mixture, beating w4ell after each addition. Stir in butter. Fold in berries. Pour into a greased 20 cm square baking pan; sprinkle with the remaining sugar. Cover and chill overnight. Remove from the refrigerator 30 minutes before baking. Bake at 180ºC or 30 to 35 minutes.