Sift flour once, measure, add baking powder and salt, and sift together three times. Heat milk , butter, and lemon rind over low flame until butter is melted (do not scald). Remove from fire and cool slightly. Add lemon juice to eggs and beat until thick and lemon-colored; add sugar gradually, and beat until light and fluffy. Add flour, alternately with warm milk mixture, mixing quickly but thoroughly. Bake in greased pan, 10x10", in moderate oven (350~) 35 minutes, or until done. Combine brown sugar, cream, melted butter, and cocoonut and mix lightly until thoroughly blended. Spread this mixture evenly over top of cake. Return cake to oven and bake 11-15 minutes longer, or until brown sugar mixture carmelizes. Cut in squares. Good warm.