To make the pastry dough, combine flour, powdered sugar, baking powder, and salt in a large bowl. Add the cold butter and mix with your fingertips or a pastry cutter until the mixture resembles coarse crumbs.

Add egg yolks, the whole egg, vanilla extract, and lemon zest. Mix until the dough comes together. Wrap in plastic wrap and refrigerate for at least 1 hour.

To prepare the custard filling, heat the milk in a saucepan with the lemon zest strips until just before boiling. Remove from heat and let it steep for 10 minutes, then remove the zest.

In a separate bowl, whisk the egg yolks with sugar until pale. Add cornstarch and mix until smooth. Slowly pour in the warm milk while whisking continuously.

Return the mixture to the saucepan and cook over medium heat, stirring constantly, until thickened. Remove from heat and stir in the vanilla extract. Transfer to a bowl, cover with plastic wrap directly on the surface, and let it cool completely.

Preheat the oven to 350°F (175°C). Grease and flour a 9-inch tart pan.

Roll out two-thirds of the chilled pastry and line the bottom and sides of the tart pan. Trim excess dough.

Fill the crust with the cooled custard. Roll out the remaining dough and place it on top, sealing the edges. Prick the top lightly with a fork.

Sprinkle the pine nuts evenly over the top. Bake for 35–40 minutes, or until golden brown.

Let the cake cool completely, then dust with powdered sugar before serving.