Step 1 In 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.