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.
- 1½–2 lb. small, white-fleshed, non-oily fish such as red mullet, or the heads and bones of larger white-fleshed, non-oily fish, such as cod
- 1 leek, trimmed, coarsely chopped, and rinsed
- 1 large tomato, halved
- 10 black peppercorns Pinch of salt
- 10 sprigs fresh flat-leaf parsley