Knead the flour, powdered sugar, butter, egg, and vanilla extract together in a mixing bowl. Once smooth, wrap the dough in plastic wrap and refrigerate for 30 minutes.
Sprinkle your work surface with flour, and roll out the dough using a rolling pin. With the help of a mini tart pan, press out individual portions to press inside each pan.
Bake in the oven for 20 minutes at 350°F.
Combine the two egg yolks with the sugar, the vanilla sugar (or 1 tsp. vanilla extract if vanilla sugar is difficult to find), and corn starch. Mix well. Heat the milk on the stove and once simmering, add the egg mixture to the pot and stir.
Once the crusts have cooled, remove them from the mini pans and add the filling.
Finally, garnish with raspberries and blueberries.