Knead the flour, cold butter, powdered sugar, cold egg, pinch of salt, ice-cold water, and vanilla extract together to form a smooth dough. Let the dough rest in the refrigerator for 1-2 hours to make it easier to roll out later.

Remove the dough from the refrigerator and roll it out on a lightly floured surface. Cut out round dough circles with the tart mold and place them in the tartelletes forms.

To ensure even baking, cover the tart crusts with parchment paper and fill them with baking beans or other weights. This process, known as "blind baking," helps the crusts bake evenly and become delightfully crispy.

Bake the tartelletes in a preheated convection oven at 160°C for about 25 minutes until blind-baked. Pay attention to your oven. After baking, remove the parchment paper and baking beans, and let the tart crusts cool completely.

Heat the milk together with the grated lemon zest and butter in a saucepan.

In another bowl, whisk the egg yolks with sugar until the mixture becomes clear and creamy. Add the cornstarch and flour and continue stirring. Also, add the lemon juice.

Slowly pour the heated milk into the egg yolk mixture while stirring continuously. Return the mixture to the saucepan and let it simmer lightly until it thickens to a creamy consistency.

Take the lemon cream off the heat and transfer it to another bowl. Cover it with foil and let it cool.

Fill the cooled lemon cream into the prepared tartelletes and spread it evenly.

Decorate the tartelletes with fresh raspberries and blueberries.