Mix well the flour, ricotta and milk, add the egg yolks and stir well once again. Whisk the egg whites with the sugar until stiff and carefully fold into the mixture. Peel and core the apples and cut into thin pieces. Put the mixture into a buttered baking tin, top with sliced apple and bake in a pre-heated oven at 180° C for 15 minutes. Sprinkle with confectioner’s sugar as desired.