Put blueberries on a sieve and defrost for 30-45 minutes. Separate 2 eggs, chill the egg whites. Cream butter, 150 g sugar, vanilla flavouring and salt with the whisk of the hand mixer. Stir in egg yolks, then alternately stir in the whole eggs and 25 g starch. Add quark and stir in. Mix 80 g flour, 50 g starch and baking powder and finally stir in briefly
Put the dough into a greased box cake tin (30 cm long, 11 cm wide, approx. 1.8 litres capacity) and spread. Set aside about 2 tbsp. of the blueberries. Mix the remaining blueberries and 20 g flour in a bowl and spread on the cake. Bake in the preheated oven, 2nd shelf from below (electric oven: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for about 1 hour. Leave the cake to cool on a cake rack for approx. 30 minutes, then carefully remove from the edge, turn onto a plate and leave to cool for approx. 2 hours
Beat the egg whites until stiff, adding 120 g sugar at the end and continue beating for about 2 minutes. Stir in lemon juice. Lift the cake onto an ovenproof dish and pour the meringue onto the cake. Spread the rest of the blueberries in small blobs and spread the meringue on the cake. Brown briefly in the preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: see manufacturer) or under the preheated grill
waiting time approx. 2 3/4 hours