Save Parmesan rinds in the freezer until you have enough to make this broth. Many grocery stores grate their own Parmesan and have rinds available for sale. Use this broth in risotto, beans, pasta dishes, soups, or even as a deglazing liquid.

Heat in a medium, dry cast-iron skillet over medium-high heat cut side down:

Cook until the onion is charred, about 5 minutes. Add the onion to a medium saucepan along with:

Add:

Bring to a boil, reduce the heat, and simmer gently, partially covered, for 2 hours. Strain and cool, then refrigerate for up to 4 days or freeze for up to 6 months. After refrigeration, there will be a fat cap on top of the broth—do not discard the fat. It is flavorful and will enrich the dishes it is added to, so simply stir it back in.