For the Pastry Crust:

1. In a bowl, combine flour, sugar, and cold butter. Use a pastry cutter or your hands to mix until it resembles coarse crumbs.
2. Add the egg yolk and mix gently. Gradually add ice water, 1 tablespoon at a time, until the dough comes together.
3. Form the dough into a disc, wrap it in plastic wrap, and chill for at least 1 hour.
4. Roll out the chilled dough on a floured surface. Line a pie dish with the dough and trim the edges.
5. Blind bake: Preheat the oven to 425°F (220°C). Line the crust with parchment paper, fill with pie weights or beans, and bake for 15-20 minutes. Remove the weights and bake for another 5 minutes until golden. Let it cool.

For the Custard Filling:

1. Heat the milk and vanilla in a saucepan over medium heat until just simmering.
2. In a separate bowl, whisk the egg yolks, sugar, and cornstarch until smooth and pale.
3. Slowly pour the warm milk into the egg mixture, whisking constantly.
4. Return the mixture to the saucepan. Cook over medium heat, stirring constantly, until the custard thickens.
5. Remove from heat and whisk in the butter until smooth. Let it cool slightly.

Assembling the Pie:

1. Pour the custard filling into the baked crust and smooth the top with a spatula.
2. Chill the pie in the refrigerator for at least 2 hours to allow the custard to set.

Serving:

• Serve chilled or at room temperature with a dusting of powdered sugar or fresh berries.