Yield: 1 1/2 quarts
In a large bowl, blend the ricotta, the squaquerone, the Parmigiano-Reggiano, the lemon zest, the pepper, nutmeg and salt to taste. Check the seasoning, stir in the egg yolk, cover and chill 2 hours or overnight before proceeding.
Remove the filling from the refrigerator and let sit at room temperature 10 minutes.
Divide the dough into 3 equally-sized balls and roll them out to the thinnest setting on a pasta rolling machine. Cut each sheet into 2-inch squares. In the center of each square, place tablespoons of the filling. Fold diagonally-opposite corners to meet each other to form the cappelletti. Place the cappelletti on a sheet tray dusted with semolina flour, and cover with clean, damp dish towels or hold in the freezer until ready to use.
Bring the chicken stock to a boil and add salt if necessary. Drop the capellatti in the chicken stock, working in batches if necessary to avoid overcrowding the pot. Cook for 2 minutes, remove from heat and serve immediately with a ladle of the broth spooned over, and topped with grated Parmigiano-Reggiano.
As you expand the well, keep pushing the flour up from the base of the mound to retain the well shape. The dough will come together when half of the flour is incorporated.
Start kneading the dough with both hands, using the palms of your hands. Once you have a cohesive mass, remove the dough from the board and scrape up and discard any leftover bits. Lightly reflour the board and continue kneading for 6 more minutes. The dough should be elastic and a little sticky. Wrap the dough in plastic and allow to rest for 30 minutes at room temperature. Roll or shape as desired.