Homemade stock infuses the deepest flavor into paella. In Spain, a classic fish stock—the kind used in shellfish paella—is typically made from a combination of small bony, non-oily soup fish (such as little red mullets), the heads and bones of larger species (such as monkfish or cod), and often a handful of Mediterranean galeras (mantis shrimp) or small crabs, and simple aromatics. This recipe doubles easily if you prefer to make a big batch and store it.
