In a mixing bowl, whisk together the all-purpose flour, powdered sugar, and salt until evenly combined.

Add the cold, cubed butter to the flour mixture and mix until it resembles coarse crumbs.

Stir in the egg yolk, then gradually add cold water, mixing until the dough holds together.

Form the dough into a ball, flatten it into a disc, wrap in plastic wrap, and refrigerate for at least 30 minutes.

In a separate bowl, whisk together the eggs and granulated sugar until smooth.

Mix in the milk, heavy cream, vanilla extract, and a pinch of salt.

Preheat the oven to 375°F (190°C).

Roll out the chilled dough to about 1/8 inch thick.

Use a round cutter to cut out circles and gently press them into a muffin tin.

Pour the egg custard filling into each pastry shell, filling them about 3/4 full.

Bake for 20-25 minutes, or until the custard is set and the tops are lightly golden.

Allow the tarts to cool for a few minutes before transferring to a wire rack.

Serve warm or at room temperature.