For the Croissant-Apple-Topfenauflauf, first peel the apples, remove the core and dice the flesh. Caramelize some sugar in a pan, add whipping cream and stir in some butter. Add apples and simmer for about 10 minutes at low temperature.
Meanwhile, beat egg whites to stiff peaks and refrigerate.
Mix curd, sugar (to taste), egg yolks and vanilla extract.
Cut croissants into cubes and add to curd along with apple cubes (save caramel sauce). Fold in beaten egg white. Pour the mixture 2/3 full into buttered, ovenproof ramekins and place in the oven at 180 °C in a bain-marie for about 20 minutes. Do not open the oven door in between!
Serve the croissant-apple-hot cheese soufflé with caramel sauce.