Circle B Kitchen
The recipe calls for a pound of Parmesan rinds, which admittedly would take a while to save up, so feel free to make a half recipe at a time. It freezes beautifully, and as I mentioned, using an ice cube tray means you can conveniently pull out just as much as you need. I made a half batch and didn't reduce it down quite as far as half (I partially covered it as it simmered). From 4 cups of water, I ended up with 2 3/4 cups of broth. Also, I felt like like it needed a little salt to really bring out the parmesan flavors, so feel free to add a little to the finished broth.
Recipe from Bon Appetit
Makes about 4 cups
2 tablespoons olive oil
1 onion, peeled, quartered
1 head of garlic, halved crosswise
1 bunch thyme
1 bay leaf
3–4 parsley sprigs
1 teaspoon black peppercorns
8 cups of water
1 cup dry white wine
1 pound Parmesan rinds
(salt as desired; I used between 1/2 to 1 teaspoon salt per cup of broth)
Heat oil in a large saucepan over medium-high heat. Cook onion, garlic, thyme, bay leaf, parsley, and peppercorns, stirring often, until garlic is deep brown, about 5 minutes. Add wine, bring to a simmer, and cook, scraping up any brown bits, until liquid is reduced by half, about 4 minutes.
Add Parmesan rinds and the water; bring to a boil. Reduce heat and simmer, stirring occasionally to prevent cheese from sticking to bottom of pot, until broth is flavorful and reduced by half, about 2 hours (see headnote).
Strain through a fine-mesh sieve into a large bowl (or an airtight container if making ahead). Salt as desired and cool completely before freezing.