For the curd soufflé, strain the curd, add the egg yolks, cornflour, a pinch of salt, vanilla sugar, grated lemon zest and sour cream and stir until smooth.
Butter one or more suitable soufflé molds and sprinkle with sugar.
Place a suitable water bath in the oven at 180 °C.
Beat the egg whites with the sugar until stiff and fold into the curd mixture.
Fill about 2/3 of the soufflé mixture into the molds, place them in the water bath and poach for about 30 minutes.
Turn out the soufflé and serve quickly.