In a large bowl, sift together 1½ cups all-purpose flour and 2 tablespoons powdered sugar until evenly blended.

Add 6 tablespoons cold, cubed unsalted butter and work with fingertips until mixture resembles coarse crumbs.

Stir in 1 egg yolk with 1 to 2 tablespoons cold water until dough just comes together; avoid overmixing. Wrap and chill for 30 minutes.

In a saucepan, gently heat 1 cup whole milk with ¼ cup sugar over medium heat until sugar dissolves and mixture steams.

Whisk 3 egg yolks and 1 tablespoon cornstarch in a bowl until smooth and pale.

Gradually whisk hot milk into egg mixture, then return to pan. Cook over low heat, stirring constantly until custard coats the spoon, about 2 minutes.

Preheat oven to 350°F (175°C). Roll chilled dough to 1/8-inch thickness, line six 3-inch tart tins, trim edges, and prick bottoms lightly with a fork.

Line shells with parchment and weights; bake for 15 minutes until edges set. Remove weights, pour custard, then bake for 12–15 minutes until custard holds and edges are lightly golden.