Grease only the bottom of a springform pan (26 cm Ø) and sprinkle with the breadcrumbs. Wash and sort the blueberries and drain them well. Preheat the oven (electric cooker: 175 °C/recirculating air: 150 °C/gas: see
manufacturer). Separate eggs. Cover the egg whites and chill.
Mix egg yolks, butter, sugar and vanilla sugar in a large bowl with the whisks of the mixer for 3-5 minutes until light creamy. Mix flour and baking powder. Alternately stir in the quark and lemon juice.
Beat the egg whites until stiff and fold into the dough with a whisk. Then fold in half the blueberries. Fill the dough into the tin and bake in a hot oven for 60-70 minutes.
Spread with jam about 15 minutes before the end of the baking time and cover with aluminium foil. Leave the cake to cool slightly in the oven, then remove and cover with the remaining fresh blueberries. Let the cake cool down.