Melt the butter and sugars together, then pour into an 8" cake pan.
Toss the apples with the lemon juice (to prevent browning), then arrange in the pan in a pretty pattern and sprinkle with the raisins and nuts. Bake at 375F for 30 minutes.
Meanwhile, combine the sugar and yolks and mix until pale and creamy yellow. Add the lemon juice and potato starch, mix well then set aside.
In another bowl, beat the egg whites until firm peaks form, then fold into the yolk mixture. Spread this over the hot apples, then continue baking for at least 30 more minutes or until tester comes out clean.
Remove the cake from the oven and allow it to sit for a few minutes. Run a sharp knife along the edges to make sure the cakes edges are not sticking, then place a plate over top the cake pan, and flip!