Preheat the oven to 160 °C, grease with oil and flour a rectangular shape for the cake. Bring butter and cheese to room temperature.
Whisk cheese and butter until fluffy. Continuing to whisk, first pour the sugar in a thin stream, then one by one beat the eggs and add a spoon of sour cream.
Melt the chocolate in a water bath or microwave. Divide the dough into 2/3 and 1/3. Just divide the flour. Add chocolate and 2/3 flour to 1/3 of the dough. Add 1/3 of the flour to 2/3 of the dough. Stir first separately.
Now pour the white dough into the prepared baking dish. Pour in the white chocolate dough and lightly stir with a chopstick to get "marble" patterns.
Put the mold in the oven and bake for about 35 minutes. the brownie inside should stay moist. Cool on a grid, turn on a dish, decorate to your taste and serve.