Preheat the oven at 175 °C. Butter the sides and the bottom of a 20x33 cm (8x12 inch) pan and line it with baking paper.
Put the bittersweet chocolate and butter in a large bowl and set it over a saucepan of simmering water. Stir occasionally, until the chocolate and butter are completely melted.
Turn off the heat and add the sugar. Whisk until the sugar is completely combined, then remove from the saucepan and wait for the mixture to cool for about 10 minutes.
Whisk in the eggs, one by one.
Add vanilla bean powder, baking soda, salt, and a third of the flour to the chocolate mixture. Whisk well. Add the rest of the flour and whisk again until the mixture is smooth.
Stir in the bittersweet chocolate chips.
Pour the batter in the prepared pan and sour cherries. Don't press them in.
Bake for about 25 minutes or until the edges start to pull away from the sides of the pan. Keep in mind that it is better to slightly underbake than overbake brownies.
When you take the brownies out of the oven sprinkle them with white chocolate chips. Here you can press in a little if you like.
Wait for the brownies to cool completely, then lift them up together with the baking paper and cut them into 15 pieces.
Store in a plastic wrap or air-tight container at room temperature for up to 4 days.