Wash and clean 250 g strawberries and cut them in half or quarters depending on size. Grease the bottom of a springform pan (26 cm Ø) very well. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer).
Separate eggs. Beat egg whites until stiff. Mix the egg yolks, 150 g butter, sugar, vanilla sugar and 1 pinch of salt in a large mixing bowl with the whisks of the mixer for about 5 minutes until light creamy. Mix the pudding powder, starch and baking powder and stir well into the egg yolk mixture with the quark and lemon juice.
Fold in the beaten egg white in portions.
Carefully fold in the prepared strawberries. Pour the mixture into the springform pan, smooth it down and bake in a hot oven for 60-70 minutes.
Stir the jam until smooth. Spread the cake evenly about 15 minutes before the end of the baking time, cover with foil and bake to finish. Turn off the oven and let the cake rest in the oven for about 30 minutes.
Take out, remove foil and let the cake cool down on a cake rack.
Wash, clean and halve the rest of the strawberries. Carefully remove the cake from the mould. Spread strawberries on top and dust with icing sugar.