Grease a small rectangular baking dish or a rectangular baking frame with a size of approx. 20 x 25 cm generously with butter and preheat the oven to 175 ° C top and bottom heat.
Dough:
Finely chop the chocolate and melt it together with the butter in a double boiler.
Whip the sugar, salt and eggs until frothy. Sieve the flour, baking powder and cocoa powder and carefully fold them into the egg mixture together with the remaining ingredients.
Cheescake filling:
Put all ingredients in a bowl and stir to a smooth mass.
Completion:
Pour the dough into the mold and smooth it out. Pour the cheescake filling onto the batter using a spoon. To create the marble pattern, lift the cheescake filling under the brownie dough with spiral movements. Finally, distribute the blueberries on the dough and bake it for about 40 - 45 minutes.