In a mixing bowl, combine chilled diced butter, all-purpose flour, granulated sugar, one large egg, egg yolk, vanilla extract, and a pinch of salt. Blend until it resembles coarse crumbs. Knead gently until smooth.

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

In a saucepan, heat whole milk until just below boiling. In a separate bowl, whisk together egg yolks, granulated sugar, cornstarch, and lemon zest until smooth.

Pour hot milk into the egg mixture while whisking continuously, then return to saucepan over medium heat, stirring until thickened, about 5-7 minutes.

Remove from heat, stir in unsalted butter and vanilla, and let the custard cool to room temperature before refrigerating.

Preheat oven to 350°F (175°C).

On a floured surface, roll out chilled pastry dough to about ¼ inch thickness.

Grease a tart pan, line it with the dough, prick the base, and let any excess hang over the edges.

Pour the cooled custard into the pastry shell, leveling it out evenly.

Sprinkle pine nuts or sliced almonds on top of the custard filling and lightly press them in.

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

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

Dust with powdered sugar before serving.