Make the pasta frolla

1. Combine the flour, sugar, baking powder, salt, and lemon zest in a bowl. Add the cold, cubed butter and rub in with your fingertips until the mixture resembles coarse breadcrumbs.
2. Add the egg yolks and mix together, adding cold water one tablespoon at a time, just until the dough comes together. Do not overwork it.
3. Shape into a disc, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Make the filling and assemble

1. In a saucepan, combine the wheat kernels, 2 tablespoons of the sugar, butter, milk, lemon zest, and vanilla (split the pod, scrape the seeds, and add both seeds and pod). Cook over medium-low heat for about 1 hour, stirring occasionally, until the mixture resembles creamy oatmeal. If you prefer a very smooth filling, blend briefly with an immersion blender after cooking.
2. Pour into a bowl and let cool completely.
3. In a large bowl, combine the cooled wheat mixture, ricotta, remaining sugar, candied fruits, egg yolks, and orange flower water. Mix well.
4. Beat the egg whites to stiff peaks, then gently fold them into the filling with a spatula.
5. Preheat the oven to 170–180°C (340–355°F) and position the rack in the middle.
6. Roll out ¾ of the pasta frolla to 5 mm (¼ inch) thickness. Use it to line the bottom and sides of a 25 cm (10-inch) springform pan lined with parchment paper. Edges should be slightly thicker. Prick the bottom with a fork 4–5 times.
7. Pour the filling into the shell.
8. Roll out the remaining dough and cut into strips about 5 mm (¼ inch) wide. Lay them in a lattice pattern over the filling.
9. Bake for about 50 minutes. Turn off the oven, slightly open the oven door, and leave the pastiera inside to cool gradually.
10. Once cool, unmold, cover with a clean cloth, and rest on a wire rack for at least 12 hours. Just before serving, dust generously with powdered sugar.