Mix the egg yolks, butter, and ½ c of the sugar. Stir in the cake meal and potato starch. Pat into a 9×13 pan. Spread with jam. Bake at 350° for 10 minutes. Meanwhile, beat the egg whites until stiff and add the remaining ½ c of sugar. Spread this meringue mixture over the partially baked dough. Finish baking at 350° for 25 minutes. Cool and cut into squares.