Cut the rhubarb stalks into thin slices and sprinkle with 1 tablespoon of sugar. Mix the quark, egg yolk and vanilla sugar together. Beat the egg whites with a pinch of salt until stiff. Let the remaining sugar trickle in while whipping, then fold the egg whites into the quark.
Just grease the bottom of a gratin dish, add half of the sugared rhubarb and top it with the quark cream. Cover with the remaining rhubarb slices. Bake in the preheated oven at 200 ° C on the middle rack for about 25 minutes until the soufflé is golden brown.