Preheat the oven to 160 °C, grease a rectangular pie pan with butter and flour. Bring the butter and cheese to room temperature.
Whisk the cheese and butter until fluffy. Continuing to beat, first add sugar in a thin stream, then beat the eggs one by one and add a spoonful of sour cream.
Melt the chocolate in a water bath or in a microwave oven. Divide the dough into 2/3 and 1/3. Just divide the flour. Add the chocolate and 2/3 of the flour to 1/3 of the dough. Add 1/3 of the flour to 2/3 of the dough. Mix separately first.
Now pour the white dough into the prepared baking dish. Pour in the white chocolate dough and mix lightly with a chopstick to make "marble" patterns.
Place the mold in the oven and bake for about 35 minutes. the brownie inside should stay moist. Cool on the grill, put on a platter, decorate to your liking and serve.
