In a large mixing bowl, combine cold unsalted butter, all-purpose flour, granulated sugar, egg, egg yolk, vanilla extract, and a pinch of salt. Blend until the mixture resembles coarse crumbs. Form the dough into a ball, wrap it in plastic, and refrigerate for at least 30 minutes.

Heat whole milk in a saucepan until just below boiling. While heating, whisk together egg yolks, sugar, cornstarch, and lemon zest in a separate bowl. Slowly pour hot milk into the egg mixture while whisking continuously.

Return the egg and milk mixture to the saucepan. Cook while whisking constantly until thickened, about 5-7 minutes. Stir in unsalted butter and a splash of vanilla.

Transfer the custard to a bowl and cover with plastic wrap to prevent a skin. Let it cool at room temperature for about 20-30 minutes.

Preheat the oven to 350°F (175°C).

Once the dough has chilled, sprinkle flour on a surface and roll out to about ¼ inch thickness.

Grease a tart pan with butter, lay the rolled pastry into the pan, trim excess, and prick the base with a fork.

Pour the cooled custard into the pastry shell, spreading it evenly.

Sprinkle pine nuts or sliced almonds over the custard filling.

Bake for 30-35 minutes until the crust is golden brown and the custard is set with a slight jiggle.

Let the tart cool in the pan for 30 minutes, then transfer to a wire rack to cool completely.

Before serving, dust with powdered sugar using a fine mesh sieve.