Line the bottom of a springform pan (26 cm Ø) with baking paper. Melt butter in a pot, let it cool down lukewarm. Separate the eggs. Beat the egg white with the whisk of the mixer until stiff. Add 175 g sugar and 1 pinch of salt.
Stir in the egg yolks one by one. Mix flour with baking powder, fold in carefully. Stir in butter.
Fill half of the mixture into the springform pan and smooth it down. Spread 100 g frozen blueberries on top. Spread the rest of the mixture and another 100 g blueberries (let the rest of the blueberries thaw) on top of it.
Bake in the preheated oven (electric oven: 200 °C/circulating air: 175 °C/gas: see manufacturer) for 40-45 minutes. Let the sponge cake cool slightly in the mould, remove from the mould and let it cool down on a cake rack.
Mix pudding powder and 4 tablespoons of sugar. Stir with 100 ml milk and 1⁄4 l advocaat until smooth. Boil 700 ml milk. Remove from heat, stir in the pudding powder. Bring to the boil again while stirring, simmer for about 1 minute.
Cut the bottom twice horizontally. Place a cake ring around the lower cake base. Spread half of the pudding on it. Place the middle cake base on top. Spread the rest of the pudding on top, cover with the top cake layer and press down gently.
Chill the cake for about 2 hours.
Whip the cream until stiff. Pour approx. 5 tbsp. into a piping bag with perforated spout. Spread the rest of the cream all around the cake and decorate with cream tuffs. Spread 5 tbsp. advocaat on the cake. Chill the cake for about 30 minutes.
Stir jam until smooth and mix with the defrosted blueberries. Spread on the tuffs just before serving.