Preheat the oven to 180°C (350°F).

To prepare the crust, combine the flour, butter, and sugar in a bowl. Use your hands or a pastry cutter to mix until it resembles coarse crumbs. Add cold water and knead into a dough. Chill for 15 minutes.

Roll out the dough and cut into small circles to fit into mini tart pans. Press the dough into the pans and prick the bottoms with a fork. Bake for 10-12 minutes or until golden. Let cool.

For the filling, heat the cream and sugar in a saucepan over medium heat until warm. In a bowl, whisk the egg yolk and vanilla, then slowly pour the warm cream mixture into the yolk, whisking constantly.

Return the mixture to the saucepan and cook over low heat until thickened. Remove from heat and let cool.

Spoon the custard into the cooled tart shells and top with fresh mixed berries. Chill for 30 minutes before serving.