Step 1In a large stock pot, cover the bones with the cold water. Bring to a boil, then reduce the heat to a simmer, skimming any scum from the surface of the broth. Add the onions, celery, carrots, parsley stems and Parmigiano rinds and gently simmer, loosely covered, for 2 hours (while the broth is simmering, prepare the pasta and filling). Strain, discarding the solids and any fat that has risen to the top. Season the broth with 1 teaspoon salt, or to taste. Cool, then refrigerate until ready to prepare the final dish.
Step 1In a very large bowl, whisk together the flour and salt. Make a well in the center of the flour and add the eggs. Working with your hands, slowly incorporate the flour with the eggs to form a dough. If the mixture feels a little dry, add water, a tablespoon at a time, just until the flour is evenly incorporated. The dough will be very firm (it will relax and soften as it rests in the refrigerator). Knead the dough a minute or two to smooth out some of the roughness, then cover tightly in plastic. Refrigerate the dough at least 1 to 2 hours, up to 1 day.
Step 1In a large sauté pan, brown the pork and chicken with the butter over medium heat until cooked through. Add the white wine, scraping any flavoring from the bottom of the pan, then remove from heat and set aside to cool. Place the cooled meat in a food processor with the prosciutto, mortadella, Parmigiano Reggiano, egg yolks and ricotta. Season with 1/4 teaspoon salt, 1/8 teaspoon pepper and a pinch of nutmeg, or to taste. Pulse the mixture until the meat is ground and the filling ingredients are fully combined.
Step 1Prepare the tortellini: Roll the pasta out as thinly as possible. Cut the pasta into roughly 1-inch squares. Place a small ball (about 1/4 teaspoon) of filling on the pasta, then fold the pasta over to form a triangle, sealing the edges (if the edges won't stick, wet them with a little water). Bring the outer ends of the triangle together to form the tortellini shape, pressing the ends together to seal. Repeat with the remaining pasta and filling. (This can easily make 400 or more tortellini depending on the size of the shaped pasta.)
Step 2Bring the broth to a boil. Add the pasta (this will need to be done in batches), and cook until the pasta is just tender, about 3 minutes.
Step 3Serve 25 to 30 tortellini in broth for each guest, sprinkling over a little more grated Parmigiano Reggiano before serving.