Cream the butter, sugar and vanilla sugar until fluffy, gradually add the two eggs, flour, corn flour and baking powder. Then pour the mixture into a buttered cake tin. Peel and quarter the apples, place on the cake and bake in the oven at approx. 170 °C for 35 to 40 minutes. Cream: mix together the egg yolks, mascarpone, sugar and vanilla sugar. Before serving, whisk the egg whites until stiff, fold in to the cream and spread the mixture on top of the cooled cake.