Chopping chocolate. Cut butter into pieces. Melt the chocolate and butter in a pot at low heat. Mix flour, cocoa and baking powder. Beat the eggs, brown sugar and salt in a bowl with the whisk of the hand mixer for about 5 minutes until creamy.
Remove the chocolate-butter mixture from the heat and immediately pour into the egg mixture and stir in. Quickly fold the flour mixture into the chocolate-egg mixture.
Put the dough into a greased, square springform pan (24 x 24 cm) and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 25 minutes.
Take out and let it cool down on a cake rack. Wash and sort the blueberries and drain them well. Stir the jam until smooth, stir into the blueberries.
Stir cream cheese with sugar until smooth. Mix cream consistency and vanillin sugar, whip cream until stiff and allow the cream consistency mixture to trickle in. Fold the cream into the cream cheese. Remove the base from the mould, place the mould ring around the base again.
Spread the cream on the floor. Spread the blueberry mixture on top and spread. Chill for about 2 hours. Cut into pieces.