Cut butter into pieces. Knead butter, flour, 125 g sugar, salt and egg first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Wrap the dough in foil and chill for about 30 minutes. Grease the fat pan of the oven (32 x 39 cm) and roll out the dough on top, pulling up the edge of the pan by about 1.5 cm. Prick several times with a fork and bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 15 minutes.
In the meantime, wash and drain the currants and use a fork to remove the berries from the panicles. Beat the egg whites until stiff, adding 200 g sugar and vanillin sugar. Fold in currants and hazelnuts. Spread the meringue mixture over the hot cake and bake for another 20 minutes at the same temperature, covering if necessary. Let the cake cool down, dust with icing sugar if necessary and cut into 24 pieces
Waiting time approx. 1 hour