Prepare the Tart Crust:

1. In a food processor, combine flour, sugar, and salt. Add cold butter and pulse until the mixture resembles coarse crumbs.
2. Add egg yolk, cold water, and vanilla extract, and pulse until the dough just comes together.
3. Wrap the dough in plastic wrap and chill for 30 minutes.
4. Preheat oven to 350°F (175°C).
5. Roll out the dough on a lightly floured surface and cut into circles to fit a mini tart pan (or use a muffin tin). Press dough into the molds.
6. Prick the bottoms with a fork, then bake for 12-15 minutes, or until golden brown. Let cool completely.

Make the Pastry Cream:

7. In a saucepan over medium heat, heat milk until warm but not boiling.
8. In a bowl, whisk together sugar, egg yolks, and cornstarch until smooth.
9. Gradually pour the warm milk into the egg mixture, whisking constantly.
10. Return the mixture to the saucepan and cook over medium heat, stirring until thickened.
11. Remove from heat, stir in vanilla extract and butter, then let cool.

Assemble the Mini Fruit Tarts:

12. Spoon pastry cream into each cooled tart shell.
13. Arrange fresh fruit on top in a decorative pattern.

Make the Glaze (Optional):

14. Heat apricot jam and water in a small saucepan until smooth. Brush lightly over the fruit for a glossy finish.