Clean, wash and drain the rhubarb and cut it diagonally into thick slices. Sprinkle 2 tablespoons of sugar over it and let it steep a little. Melt the fat for the crumbles. Knead 250 g flour, 125 g sugar and vanillin sugar with the lukewarm liquid fat to a crumbly mass. Mix quark, remaining sugar, milk, oil, salt and lemon peel. Mix the remaining flour and baking powder and stir half into the quark mixture.
Add the remaining flour and knead into a smooth, supple dough. Grease a baking tray (approx. 39x32 cm) and sprinkle with breadcrumbs. Roll out a thin layer of quark oil dough and prick it several times with a fork. Peel bananas, cut them into slices and turn them in lemon juice. Drain and spread on the dough together with the rhubarb. Sprinkle the crumbles evenly over the fruit and bake in the preheated oven (electric range: 200 °C / gas: level 3) for 35-40 minutes and let cool off