In a saucepan, heat the milk over medium heat until steaming but not boiling. Remove from heat.

In a separate bowl, whisk the egg yolks with sugar until pale and slightly thickened. Add the cornstarch and mix until smooth.

Slowly pour the hot milk into the egg mixture while whisking constantly to temper the eggs.

Pour the mixture back into the saucepan and cook on low heat, stirring constantly, until thickened (about 5–7 minutes).

Stir in the vanilla extract and lemon zest (if using). Cover the surface of the cream with plastic wrap and chill in the refrigerator.

In a large bowl, mix the flour, sugar, baking powder, and salt.

Add the cubed cold butter and work it into the flour until the mixture resembles coarse crumbs.

Add the egg and mix until a soft dough forms. Divide the dough into two balls—one slightly larger than the other.

Wrap both dough balls in plastic wrap and chill in the refrigerator for 30 minutes.

Preheat the oven to 350°F (175°C). Line a baking pan with parchment paper or grease it lightly.

Roll out the larger dough ball and press it into the prepared pan, covering the base and sides evenly.

Pour the chilled pastry cream into the crust, spreading it out smoothly.

Roll out the second dough ball and place it over the cream to cover. Press the edges gently to seal.

Prick the top layer of dough with a fork to allow steam to escape during baking.

Sprinkle the pine nuts evenly over the top.

Bake in the preheated oven for 35–40 minutes, or until the top is golden brown.

Let the cake cool completely in the pan.

Once cooled, dust the top generously with powdered sugar and serve.