For the curd raspberry blueberry tart, first prepare the shortcrust pastry. Quickly knead flour, powdered sugar, margarine, egg and salt into a dough. Let the dough rest for 1/2 hour. Roll out the dough and place it in a buttered and floured tart pan, prick it a few times with a fork and pre-bake at 175 °C for about 10 minutes.
In the meantime, for the filling, whisk egg yolks, powdered sugar, lemon zest and vanilla sugar until foamy. Stir in curd cheese and cornstarch. Pour curd mixture into tart pan and bake for about 30-35 minutes.
When cool, puree the raspberries and blueberries and stir in the powdered sugar. Prepare gelatin according to package directions and stir into the raspberry-blueberry mixture. Then spread on top of the pot tart.
Refrigerate the curd cheese raspberry blueberry tart until the raspberry blueberry mixture has gelled.