Separate eggs. Beat the egg whites and salt with the whisks of the hand mixer until stiff, chill. Whisk butter and 175 g sugar with the whisk of the hand mixer until white-creamy. Stir in the egg yolks one after the other. Stir in 75 g yoghurt. Mix flour and baking powder and stir in briefly. Carefully fold in 3 portions of beaten egg white
Grease the fat pan of the oven (32 x 39 cm) and dust with flour. Put the dough into the fat pan and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 20 minutes. Take out of the oven and let cool down
In the meantime, soak gelatine in cold water. Sort blackberries. Puree 100 g blackberries with 30 g sugar in a tall container. Whip the cream with the whisk of the hand mixer until stiff. Squeeze gelatine well. Melt with 50 g yoghurt in a pot. Place the rest of the yoghurt in a bowl and mix with 30 g sugar and the gelatine-yoghurt mixture. Carefully fold in the cream. Remove half of the mixture and fold in pureed blackberries. Spread both creams alternately on the dough and mix with a fork until streaky. Spread the rest of the blackberries on top and chill for about 2 hours. Chop the pistachios. Decorate the cake with them and cut it into about 12 pieces
waiting time approx. 2 1/4 hours