In a large bowl, sift together the flour and baking powder.

Add the sugar, vanilla extract, lemon zest, and a pinch of salt.

Cut in the cold butter with a pastry cutter or your fingertips until the mixture resembles coarse crumbs.

Add the eggs and egg yolk, and mix quickly to form a dough.

Shape the dough into a ball, wrap it in plastic wrap, and refrigerate for at least 30 minutes.

In a saucepan, bring the milk, vanilla bean (split and scraped) or vanilla extract, and lemon zest to a boil. Remove from heat and let infuse for 10 minutes.

In a medium bowl, whisk together the egg yolks and sugar until pale and creamy.

Add the cornstarch to the egg mixture and mix well.

Remove the vanilla bean and lemon zest from the milk. Gradually pour the milk into the egg mixture, whisking constantly.

Pour the mixture back into the saucepan and cook over medium-low heat, stirring constantly, until the cream thickens.

Transfer the pastry cream to a bowl, cover with plastic wrap (pressing it directly onto the surface to prevent a skin from forming), and let cool completely.

Preheat the oven to 350°F (175°C).

On a lightly floured surface, roll out the dough to about 1/8 inch thickness.

Line small tartlet molds (or muffin tins) with the dough, pressing it into the molds and trimming any excess.

Fill each mold with the cooled pastry cream.

Roll out more dough and cut into rounds to cover the filled molds. Press the edges to seal.

Brush the tops with a little beaten egg mixed with a splash of milk.

Bake for about 20-25 minutes, or until the pasticciotti are golden brown.

Allow to cool slightly before removing from the molds.