Heat whole milk, lemon zest, and vanilla in a pan over medium heat until small, slow bubbles appear, just before boiling. Remove from heat; let stand.

Whisk egg yolks and sugar until pale and thick. Sift in cornstarch; whisk slowly until completely smooth.

After the milk rests about 10 minutes, slowly whisk 1/3 into the yolks, whisking constantly to prevent scrambling.

Return the egg mixture to the remaining milk. Cook over low heat, stirring constantly and scraping the bottom, until thickened and bubbling.

Once thick and bubbling for a couple of minutes, stir in optional pine nuts. Transfer to a shallow dish; press plastic wrap onto the surface to prevent a skin while cooling.

For pastry, whisk sifted flour, cornstarch, sugar, baking powder, and salt in a large bowl. Separately whisk olive oil, milk, vinegar, and lemon zest.

Combine wet and dry mixtures with a fork. Knead by hand for just 3 to 4 minutes until a smooth ball forms; do not overwork.

Wrap dough in plastic; refrigerate for 30 to 45 minutes.

After 45 minutes, preheat oven to 360°F (180°C). Grease and flour the tart pan.

Divide dough into 2/3 and 1/3 portions. Roll the larger portion between two parchment sheets to about 5 mm thick.

Line the tart pan with rolled dough. Briefly whisk cooled custard; pour into the crust.

Roll remaining dough for the top. Cover with a solid disk and cut 7 steam slashes, or cut strips for a lattice.

Bake on the middle rack for 40 to 45 minutes until golden brown. Move to the lowest rack for the last 5 minutes to cook the bottom evenly and keep the filling creamy.

Rest overnight to let the cornstarch set before serving.