Mix 500 g flour, baking powder, sugar, vanilla sugar and 1 pinch of salt in a mixing bowl. Add quark, butter in flakes, 2 eggs and 1 tablespoon rum. All this
Stir the poppy seed bake and 1 egg. Lightly dust a large sheet of baking paper with flour. Roll out the dough into a rectangle (approx. 40 x 45 cm). Spread the poppy seed mixture on it, spreading a little thinner at the edges.
Roll the dough from both long sides towards the middle. Press the two ends well together. Cut both strands slightly at regular intervals.
Lift the wrapped cake together with the baking paper into a large flat roast goose or a roast goose lid (approx. 39 cm long). Bake in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2) for approx. 30 minutes.
Whisk 1 egg yolk and cream. Spread the wrap cake with it and bake for another 20 minutes.
Mix icing sugar, 1 tablespoon rum and lemon juice to a thick icing. Spread the hot wrap cake thickly with it and let it cool down. Serve with butter as desired.