Combine the flour, powdered sugar, and salt in a food processor. Pulse briefly to mix.

Add the cold cubed butter and pulse 8 to 10 times until the mixture resembles coarse breadcrumbs with no large butter chunks visible.

Add the egg yolks, lemon zest, and vanilla extract. Pulse just until the dough comes together into a rough ball. Do not overwork it.

Turn the dough onto a lightly floured surface, press into a flat disc, and divide into two pieces, one slightly larger than the other (60/40 split). Wrap each in plastic wrap and refrigerate for at least 1 hour.

Pour the milk into a medium saucepan. Add the lemon zest and vanilla extract. Heat over medium until small bubbles appear at the edges, then remove from heat and let infuse for 5 minutes.

Whisk the egg yolks and sugar in a bowl until pale and slightly thickened, about 2 minutes. Whisk in the cornstarch until no lumps remain.

Slowly pour the warm milk into the egg mixture in a thin stream, whisking constantly. Pour everything back into the saucepan.

Cook over medium-low heat, stirring constantly with a wooden spoon or silicone spatula, until the cream thickens visibly and falls slowly from the spoon in a ribbon, about 6 to 8 minutes. It will look lumpy briefly before it smooths out - keep stirring.

Remove from heat. Stir in the butter until melted. Pass the cream through a fine-mesh sieve into a clean bowl. Press plastic wrap directly onto the surface and refrigerate until fully cold, at least 2 hours.

Heat the oven to 175 C / 350 F. Butter and flour a 9-inch (23 cm) tart tin with a removable base.

Remove the larger dough disc from the fridge. Roll it between two sheets of parchment to a circle about 3 mm thick and large enough to line the tin with a slight overhang.

Carefully lift the dough into the tin, pressing it gently into the base and sides. Trim the overhang to about 1 cm above the rim. Refrigerate the lined tin for 15 minutes.

Spoon the cold pastry cream into the crust and spread it evenly with a spatula, leaving a 1 cm border at the edge.

Roll the smaller dough disc between two sheets of parchment to a circle that fits the top of the tart. Peel off the top sheet of parchment, flip the dough over the filled tart, and peel off the remaining parchment.

Press the edges together firmly to seal. Trim any excess with a sharp knife. Brush the top crust with egg wash.

Scatter the pine nuts evenly over the top and press them very lightly into the crust so they don't roll off.

Bake for 35 to 40 minutes until the crust is pale gold and the pine nuts are lightly toasted. The center should feel just barely set when pressed.

Transfer to a wire rack and cool completely at room temperature, at least 2 hours, before removing from the tin. Dust with powdered sugar just before serving.