Spread soufflé molds or the like with melted butter and sprinkle with sugar.
Mix the curd cheese with egg yolk, lemon zest, orange liqueur and vanilla sugar until smooth. Beat the egg whites with salt and sugar until stiff. Carefully fold the egg whites under the curd mixture and carefully pour everything into the molds.
Bake in the oven at 190 ° C (preheated) in a water bath for 15-20 minutes.