Pastry Dough: 

1. In a large bowl, combine the flour, baking powder, sugar, and salt. Wisk to combine. 
2. Beat the egg in a small bowl with the lemon zest.
3. Add the egg and butter and cut them into the flour mixture in a food processor or with a fork or pastry cutter until the mixture resembles coarse breadcrumbs.
4. Mix the ingredients until the dough comes together. If the dough is too dry, add some cold water, one teaspoon at a time, until it forms a cohesive ball.
5. Turn the dough onto a lightly floured surface and knead it gently until a smooth dough ball forms. Roll the dough out using a rolling pin until about ¼ inch (½ cm) thick.
6. Grease an 8-10 inch tart pan with/a removable bottom with butter or cooking spray, lay the pastry over the pan, and tuck the edges until it fits evenly. Roll the rolling pin over the tart pan to discard any excess dough from the edges (you can also trim the edge with a knife). Poke the base with a fork, cover with plastic wrap, and place it back in the fridge for 30 minutes.

Pastry Cream

1. In a bowl, whisk together the egg yolks and sugar until pale yellow and creamy; use an electric mixer. Add the cornstarch and mix well.
2. In a saucepan, heat the milk with vanilla bean (or extract) and lemon zest until it just starts to simmer. Remove from heat.
3. Slowly pour the hot milk into the egg mixture, whisking constantly to avoid curdling.
4. Pour the mixture back into the saucepan and cook over medium heat, stirring continuously until the custard thickens. This should take about 5-7 minutes. Once thickened, remove from heat and transfer the pastry cream to a clean bowl. Place plastic wrap directly on top of the cream so a skin doesn’t form. Set aside. 

Assemble the Torta della Nonna:

1. Preheat your oven to 350°F (180°C).
2. Soak pine nuts in water for 5-10 minutes then drain and dry. This will prevent them from browning too fast in the oven. 
3. Take out the prepared tart pan with pastry shell. Spread the cooled pastry cream over the pastry. Sprinkle the pinenuts evenly over the top of the tart. 
4. Bake in the oven for about 45 minutes or until the top is golden brown. If the pine nuts start to get too dark gently tent with tinfoil and finish baking. 
5. Allow the Torta della Nonna to cool completely before serving. Remove from tart case and place on a serving plate or platter. Dust with powdered sugar before serving.