1 Preheat the oven to 180°C (approximately 350°F).
2 For the cake layer: Separate the eggs and whisk the egg yolks with the half of the sugar until light and frothy. Beat the egg whites with a pinch of salt until soft peaks form. Gradually add the remaining sugar and beat until stiff and glossy. Fold the egg whites into the yolk mixture, sift in the flour and cornstarch and mix until smooth.
3 Pour the mixture into a springform pan lined with parchment paper and bake for 15-20 minutes, until a toothpick inserted comes out clean.
4 Remove from the oven and allow to cool completely on a wire rack before removing from the springform pan.
5 For the crust: Crush the wholemeal crackers until finely ground. Combine with the cocoa powder and melted butter and press into the bottom of the springform pan.
6 For the cream layer: Whisk the vanilla pudding mix with 125 ml (approximately 1/2 cup) of milk. Heat the remaining milk with the sugar and bring to barely a simmer. Stir in the pudding mixture, bring to a boil, then remove from heat and allow to cool. Beat the butter with the powdered sugar until light and fluffy and fold into the cooled pudding mixture. Spread half of the mixture evenly over the wholemeal cracker crust.
7 Cut the sponge cake in half horizontally and spread the remaining cream over the bottom half. Replace the top half and place into the springform pan, on top of the crust. Transfer to the refrigerator.
8 For the filling: Rinse the blueberries and pat dry. Combine 350 grams of blueberries with 2 tablespoons of powdered sugar and mash the blueberries well. Mix in the cream cheese and quark. Soften the gelatine in cold water, then dissolve in a saucepan with 2 tablespoons of the cream cheese mixture. Stir the dissolved gelatin back into the cream cheese mixture and mix well. Beat the heavy cream with the remaining powdered sugar until stiff. Fold the whipped cream into the cream cheese mixture along with the lemon zest. Pour the mixture into the springform pan and refrigerate for about 3 hours.
9 Distribute the remaining blueberries on top of the cake and press lightly to secure. Carefully remove the cake from the springform pan, cut into slices and serve.