Make the pasta frolla

• 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.
• 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.
• Shape into a disc, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Make the filling and assemble

• 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.
• Pour into a bowl and let cool completely.
• In a large bowl, combine the cooled wheat mixture, ricotta, remaining sugar, candied fruits, egg yolks, and orange flower water. Mix well.
• Beat the egg whites to stiff peaks, then gently fold them into the filling with a spatula.
• Preheat the oven to 170–180°C (340–355°F) and position the rack in the middle.
• Roll out 3/4 of the pasta frolla to 5 mm (1/4 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.
• Pour the filling into the shell.
• Roll out the remaining dough and cut into strips about 5 mm (1/4 inch) wide. Lay them in a lattice pattern over the filling.
• Bake for about 50 minutes. Turn off the oven, slightly open the oven door, and leave the pastiera inside to cool gradually.
• 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.