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1
Make the pasta frolla. Rub the cold butter into the flour and salt until the mixture resembles coarse crumbs. Add the sugar, then the beaten eggs, and work briefly until the dough just coheres. Flatten into a disc, wrap, and refrigerate for at least 1 hour. The dough is ready when it holds together without sticking and feels cool and firm to the press.
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2
Cook the wheat berries. Place the soaked, drained wheat in a saucepan with the milk, butter, and lemon zest. Simmer over low heat, stirring occasionally, for approximately 45–60 minutes, until the grains have swollen, are tender yet retain a gentle chewiness, and the liquid has reduced to a thick, creamy residue. Remove the lemon zest. The grain-milk mixture is done when a berry pressed between two fingers yields easily but does not collapse entirely.
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3
Make the filling. Beat the egg yolks with the sugar until pale. Pass the drained ricotta through a sieve and fold it into the yolk mixture. Stir in the cooled wheat berry mixture — including its milky residue — along with the candied orange and citron peel, the orange blossom water, and the cinnamon. Whip the egg whites to soft peaks and fold them through in two additions. The filling is ready when it is uniformly smooth and carries a pronounced floral perfume from the orange blossom water.
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4
Line the tart pan. On a lightly floured surface, roll two-thirds of the pasta frolla to 4–5 mm thickness and line a deep 26 cm tart pan, pressing it gently into the corners and allowing a slight overhang. Pour in the filling to within 1 cm of the rim. Roll the remaining dough and cut seven strips of equal width; lay them across the top in a lattice pattern and press the ends firmly against the pastry rim. This is the step upon which the pastiera lives or dies: a filling under-seasoned with orange blossom water, or a lattice pressed on a warm pan, will not recover in the oven or during the rest — every element must be in place before the tart crosses the threshold of heat.
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5
Bake at 160–170 °C for approximately 90 minutes. The pastiera is done when the lattice and exposed rim are deep golden, the filling has set — it should not tremble when the pan is nudged — and the kitchen carries a warm, floral-caramel scent.
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6
Rest the tart at room temperature, uncovered, for a minimum of 24 hours and ideally 48–72 hours before cutting. During this rest the wheat berries absorb the surrounding cream, the flavours unify, and the texture transforms from loose and grainy to luscious and cohesive. A slice cut too soon will be crumbly and unresolved; the tart's true character is revealed only after patience. The pastiera is ready when a cut slice holds its shape cleanly and the filling presents as a single, unified mass.