Preheat the oven to 220 °C. Defrost the puff pastry and roll out on a floured work surface to the size of a baking tray, place on a baking tray lined with paper. Prick the dough a few times with a fork, sprinkle half of the dough with powdered sugar, bake in the oven for 12 minutes, then cool and carefully remove from the baking tray, cut into 20 to 24 rectangles. Rinse and clean the strawberries and cut them into slices. Soak the gelatine in cold water. Prepare a pudding from milk, granulated sugar and vanilla pudding powder, strain the pudding through a fine sieve and set aside. Mix the quark with a little sifted vanilla sugar, powdered sugar, yolks, cognac, juice of one lemon, lemon zest and vanilla pudding until smooth. Beat the cream until stiff. As soon as the custard begins to thicken, place in a piping bag with a smooth nozzle and pipe onto the unsweetened pastry rectangles, then top with strawberries, repeat piping and cover with the sweetened rectangles, finally pipe a cremerosette onto each slice and decorate with powdered sugar and chocolate shavings.
Good luck!