Preheat the oven to 425 degrees F.
In a mixing bowl, combine the butter and sugar and cream them together. Once they are well mixed and fluffy, incorporate the egg yolks, one at a time, and continue to beat.
In a separate bowl, combine the potato starch, flour, yeast, and salt and mix well. Combine the wet and dry ingredients, stirring just enough to blend. In a separate bowl, whip the egg whites and fold them into the mixture. Turn the batter out into a greased 9-inch round cake pan and bake for 30 minutes.
While the cake bakes, heat the butter in a medium saucepan. Add the apples, ginger, and sugar and cook until very soft, about 20 minutes. Set aside in a warm place. When the cake comes out of the oven allow it to rest 5 minutes, then invert it onto a plate. Spoon the apple compote over and serve with whipped cream on the side.