Peel the rhubarb stalks and cut into 2 cm pieces. Sprinkle with sugar in a saucepan. As soon as the rhubarb has drawn enough juice, simmer with a packet of vanilla sugar in the saucepan until soft. To let it cool down.
Mix the quark with milk, sugar and vanilla sugar and season with lemon juice. Layer the rhubarb alternately with quark in clear glasses. Refrigerate. Sprinkle with grated chocolate before serving.