For the filling: Place the farro in a large bowl and cover with cold water. Let the faro soak for 3 days, changing the water daily. On the third day, drain the grain and place them in a medium-sized pot. Cover with cold water. Bring the water to a boil over a high flame, reduce to a simmer and let simmer for 15 minutes. Drain the faro.
In a medium-sized saucepan, heat the milk over a medium flame until hot but not smoking. Add the faro, 1/2 the lemon zest, 1 pinch cinnamon, 1 tablespoon sugar, and let cook over moderate heat, stirring occasionally, until the milk is completely absorbed.
Place the ricotta in a large mixing bowl. Using a wooden spoon, mix the ricotta until the texture becomes creamy. Add the remaining cinnamon, sugar, egg yolks, the remaining lemon zest, orange flower water, and the cooked faro. Use a spatula to mix until well combined then set aside.
To make the dough: Sift the flour and sugar together then mound on a wooden cutting board or clean surface. Dig a hole in the center to form a well. Mix together the butter and egg yolks in the center of the well. Being careful not to break the outer walls of the well, incorporate the flour, eventually bringing all the flour into the dough. Keep mixing and kneading until the dough forms a homogenous mass. Knead 5 minutes more then wrap the dough in plastic wrap and let rest in the refrigerator for 30 minutes.
Preheat the oven to 350 degrees F.
Cut the dough into 2 pieces, 1 piece 3 times as large as the other. Using a lightly floured rolling pin, roll out the larger dough piece until it forms a large circle, about 11 inches in diameter and about 1/8-inch thick.
Lightly butter and flour a 9-inch round baking pan. Place the larger dough round into the baking pan, using your thumb and forefinger to tuck the dough into the bottom of the pan. The dough should come up the sides of the pan.
In the bowl of an electric mixer fitted with a whisk attachment, whisk the egg whites until they form medium-hard, glossy peaks. Using a spatula, gently fold the egg whites into the ricotta mixture. Gently place the filling into the baking pan, on top of the bottom crust.
Using the lightly floured rolling pin, roll the remaining dough into a circle 1/8-inch thick. Using a sharp knife, cut the dough into strips 1-inch wide. Use these dough strips to decorate the top of the ricotta pie, forming a lattice across the top, just as you would an apple pie.
Place the pie in the oven and bake until the dough on top is golden brown, about 1 hour. Remove from the oven and let cool to room temperature. Dust with confectioners' flour before serving.
Recipe courtesy of Mario Batali