To prepare the apples, melt the margarine and the sugars in the bottom of a deep round pan large enough to hold the apples comfortably. Arrange the apples over the sugar. Fill the core openings with walnuts and raisins. Pour the lemon juice over the apples.
Preheat oven to 375 degrees F. Bake for 30 to 35 minutes, until the apples are tender.
To prepare the batter, beat the egg yolks with the sugar in a large mixing bowl until very light. Add the lemon juice and sifted potato starch. In a clean bowl, with clean beaters, beat the egg whites until stiff but not dry; carefully fold the beaten egg whites into the egg yolk mixture. Pour the batter over the hot apples and bake for an additional 30 minutes or until the cake tests done.
Let the cake rest on a cake rack for 10 minutes before turning it out, upside down, onto a large cake plate. Serve cold.