Mash the bananas as much as possible with a fork. Then put the quark in a bowl and mix in the banana puree in 2 servings until everything is well distributed. But be careful with a spoon, not in the blender.
Then add the cocoa powder. Depending on your taste, 2 - 3 tablespoon. Usually 2 spoons are enough for me, but you can vary that depending on how chocolaty the whole thing should be and how sweet the bananas are. Possibly fold in chocolate.
You can also serve the dessert very nicely by e.g., desiccated coconut there.