Combine diced cold unsalted butter, all-purpose flour, granulated sugar, large egg, vanilla extract, and a pinch of salt in a mixing bowl. Mix until a smooth dough forms, about 5–7 minutes.

Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.

In a saucepan, gently heat whole milk over medium heat until warm. In a separate bowl, whisk together egg yolks, granulated sugar, cornstarch, and lemon zest until smooth.

Gradually pour the warm milk into the egg mixture, whisking continuously. Return to the saucepan and cook until the custard thickens, about 5–7 minutes.

Remove from heat, transfer to a bowl, and cover with plastic wrap. Allow to cool to room temperature.

Preheat your oven to 350°F (175°C).

Roll out chilled dough to about ¼ inch thick on a floured surface.

Grease a tart pan with butter and line it with the rolled-out pastry. Prick the base with a fork.

Pour the cooled custard into the pastry shell.

Sprinkle pine nuts or sliced almonds over the custard.

Bake for 30-35 minutes until golden brown and the custard is set.

Cool in the pan for about 30 minutes before dusting with powdered sugar and serving.