In a mixing bowl, combine all-purpose flour, granulated sugar, and a pinch of salt. Cut in the cold unsalted butter until the mixture resembles coarse crumbs. Add one egg yolk and cold water, mixing gently until just combined. Form into a ball, cover, and chill for 20-30 minutes.

Preheat your oven to 350°F (175°C). Roll out the dough into a circle about ¼ inch thick, fit into a tart or square pan, prick with a fork, and bake for 12-15 minutes.

In a medium saucepan, whisk together granulated sugar, cornstarch, lemon zest, and egg yolks. Gradually add whole milk, stirring continuously until thickened. Remove from heat and stir in fresh lemon juice, unsalted butter, and vanilla extract until smooth.

Pour the lemon custard into the pre-baked crust and bake for 25-30 minutes until edges are set. The center should jiggle slightly.

Let the cake cool at room temperature for an hour, then refrigerate for at least 2 hours or overnight before serving.