In a large mixing bowl, combine all-purpose flour, granulated sugar, and salt, stirring until evenly mixed. Cut in the cold unsalted butter until the mixture resembles coarse crumbs. Add the egg yolk and cold water, mixing until the dough forms. Wrap it in plastic wrap and chill in the refrigerator for 20 to 30 minutes.

Preheat your oven to 350°F (175°C). Roll out the chilled dough into a circle about 12 inches in diameter, then place it into a 9-inch pie dish, trimming the excess. Prick the bottom of the crust with a fork to prevent bubbling, then bake for 12 to 15 minutes until lightly golden. Allow to cool completely before adding the custard.

In a medium saucepan over medium heat, whisk together granulated sugar, cornstarch, and lemon zest. Gradually add whole milk while whisking to avoid lumps. Cook until thickened, about 5–7 minutes. Remove from heat and stir in lemon juice, unsalted butter, and vanilla extract until fully combined.

Pour the warm custard filling into the prepared crust, smoothing it evenly. Bake for 25 to 30 minutes until the custard is set but slightly jiggly in the center. Let it cool at room temperature for at least 30 minutes before refrigerating.

Once cooled, cover the cake and refrigerate for a minimum of 4 hours, ideally overnight. Dust with powdered sugar before serving and slice into pieces. Enjoy cold for a refreshing dessert.