Mix the flour, sugar and salt in a bowl. Add the butter and rub by hand to form a crumbly mixture. Add the quark, egg, lemon zest and juice, mix quickly to form a soft dough – do not knead, press flat. Roll out the dough between two sheets of baking paper, place the dough in the tin along with the bottom sheet of baking paper. Prick the base firmly with a fork, refrigerate for approx. 30 mins.
To blind bake
Approx. 25 mins. in the lower half of an oven preheated to 200°C. Remove from the oven, allow to cool slightly, then leave to cool completely on a rack.
Filling and topping
Combine the mascarpone, sugar and vanilla sugar. Add the cream, beat until almost stiff using the whisk on a hand mixer. Spread the mixture onto the tart base, arrange the strawberries on top.