- Heat the olive oil in a heavy 12-quart stockpot over medium heat. Add the onions, carrots, fennel, tomatoes, garlic, and the fish bones and cook, stirring occasionally, for 10 minutes. Add the parsley stalks, fennel seed, bay leaves, peppercorns, orange rind, saffron threads, and red pepper to the pot.
- Add cold water to barely cover ingredients. Bring to a low boil, reduce the heat to a simmer, and cook for 30 minutes, uncovered. (Add water if needed). Let the broth base cool enough to handle and then strain it through a large fine sieve or a colander lined with cheesecloth, pressing hard on the solids to extract all the juices.
- Cool the stock and refrigerate several hours or overnight. (The stock will keep refrigerated up to 3 days or frozen for six months.)