Whip mascarpone, quark, icing sugar, and the seeds of the vanilla bean. Don't throw away the empty vanilla bean; stick it in a jar full of sugar to get vanilla sugar, for instance.
Whip the heavy cream until stiff and fold it into the mascarpone mixture. Add lemon juice to taste.
Puree the strawberries with icing sugar to taste. Grate the white chocolate.
Assemble: Place the mascarpone cream mixture into one large dessert bowl or eight individual dessert cups. Pour the strawberry sauce over this mixture, poking a few times with a knife to allow the sauce to sink in the mascarpone mixture here and there.
Sprinkle with the grated chocolate and place in the fridge for at least two hours or until ready to serve.
I used low-fat quark, which is very common in Germany; if you cannot find it, you could replace it with cream cheese or creamy yogurt or a mixture of the two.
You can use frozen and defrosted strawberries when fresh ones are unavailable.