For the short pastry base, knead flour, cold fat in flakes, 100 g sugar, egg yolk and salt with the dough hooks of the hand mixer to a smooth dough. Cover and put in a cool place for about 30 minutes. Wash and clean the rhubarb and cut into pieces. Mix with 2 tablespoons of sugar and leave to stand for about 30 minutes. Roll out short pastry in the size of the fat pan (32x37 cm) or a deep glass sheet. Grease a baking tray and line it with baking paper. Pull up the dough on the baking tray slightly at the edge and press it in several times all around for decoration.
Prick several times with a fork, sprinkle with breadcrumbs. Spread the rhubarb on top and bake in a preheated oven (electric: 175 °C/ gas: level 2) for about 30 minutes. Shortly before the end of the baking time, beat the egg whites until very stiff, add the remaining sugar. Pour into a piping bag with a star-shaped spout and spray onto the cake in a grid pattern. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for approx. 5 minutes. Results in approx. 12 pieces