Whisk the flour, sugar, baking powder, and salt together in a large bowl. Add the cold cubed butter and rub it in with your fingertips until the mixture looks like coarse sand.

Add the egg yolks and lemon zest, then mix until the dough just comes together. Turn it out and knead briefly into a smooth ball.

Divide the dough into two disks, one slightly larger for the base. Wrap both in plastic and chill for 60 minutes.

Heat the milk and lemon zest in a 2-quart / 2 L saucepan over medium heat until steaming, not boiling.

Whisk the egg yolks, sugar, and cornstarch together in a bowl until pale. Slowly pour in the hot milk while whisking constantly to temper the yolks.

Return the mixture to the saucepan and cook over medium-low heat, whisking constantly, for 3 to 4 minutes until it thickens enough to coat the back of a spoon.

Stir in the vanilla, then press plastic wrap directly onto the surface of the cream. Cool to room temperature.

Heat the oven to 180 C / 350 F and butter a 23 cm / 9-inch tart pan with a removable bottom.

Roll the larger dough disk on a floured surface to about 3 mm thick and line the tart pan, pressing it into the edges. Trim any overhang.

Pour the cooled pastry cream into the shell and spread it evenly with a spatula.

Roll the second dough disk to the same thickness and lay it over the filling. Pinch the edges to seal and trim excess dough.

Brush the top with the beaten egg, scatter the pine nuts over the surface, and poke a few small steam vents with a knife.

Bake for 35 to 40 minutes until the crust is golden brown and the pine nuts are toasted.

Cool in the pan for 30 minutes, then transfer to a rack to cool completely. Dust with powdered sugar just before slicing.