Separate eggs. Beat the egg whites until stiff, adding sugar. Stir in egg yolk. Mix flour, baking powder and starch, sieve onto the mixture and fold in. Line a baking tray (32 x 39 cm) with baking paper.
Spread the mixture on top and bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 8-10 minutes, then remove from the oven and allow to cool. Mix yoghurt and vanillin sugar, allow gelatine to trickle in and continue stirring for approx. 1 minute. Chill the mixture for about 10 minutes until the cream starts to gel. Put aside about 2 tablespoons of blueberries for decoration. Coarsely crush half of the remaining blueberries. Whip cream until stiff and fold into the cream. First fold the whole blueberries into the cream, then lightly fold in the crushed blueberries, not completely. Cut out 16 circles (8 cm Ø) from the sponge cake. Place 8 circles on a plate and add 1-2 tablespoons of cream to each. Place the plate in a cool place for about 15 minutes, then place another circle on each, press lightly and finish with 1 tablespoon of cream.
First fold the whole blueberries into the cream, then lightly fold in the crushed blueberries, not completely. Cut out 16 circles (8 cm Ø) from the sponge cake. Place 8 circles on a plate and add 1-2 tablespoons of cream to each. Place the plate in a cool place for about 15 minutes, then place another circle on each, press lightly and finish with 1 tablespoon of cream. Put the sponge burgers in a cool place for about 1 hour. Warm up the jelly and stir until smooth. Decorate burgers with chopped pistachios, remaining blueberries and jelly