For the slices, first prepare the dough. For the dough, cream butter, sugar and egg yolks. Fold in flour, baking powder and milk. Line two baking sheets with baking paper and divide the dough between them.
For the beaten egg whites, beat egg whites and sugar until stiff, divide between the two sheets, sprinkle almond flakes on both and bake for about 20-25 minutes (will be very high and wavy).
For the cream, whip whipping cream, sour cream, vanilla sugar, a little sugar and cream stiffener until fluffy. Spread the mixture on the less beautiful dough, let it rise a little and cover with the second dough.