Cioppino

Peel and devein shrimp and reserve shells. Refrigerate shrimp until ready to use.

Thinly slice 1 1/2 onions and roughly chop remaining half. Trim fennel, remove outer layer and core, then roughly chop trimmings for shrimp stock. Thinly slice remaining fennel bulb and set aside.

Heat 1 tablespoon oil in large Dutch oven on medium. Add chopped onion and fennel trimmings and cook, stirring occasionally, until starting to brown, 7 to 10 minutes. Add tomato paste and cook, stirring, until beginning to caramelize, 2 minutes. Add shrimp shells and cook, stirring occasionally, until opaque, 3 to 4 minutes. Add parsley stems, 1 bay leaf and 4 cups cold water. Bring to a simmer, then simmer, stirring occasionally, 20 minutes.

Strain stock through fine-mesh strainer set over large measuring cup or bowl, pressing down on solids, then discard solids. You should have about 2 1/2 cups shrimp stock. Set aside until ready to use.

Wipe out Dutch oven, then heat remaining 3 tablespoons oil on medium. Add sliced onion and fennel and 1/2 teaspoon salt and cook, stirring to coat in oil. Cover and cook, stirring occasionally, until tender, 10 to 12 minutes. Add garlic and cook, stirring occasionally, 2 to 3 minutes. Add wine and simmer until reduced by half, 1 minute. Add shrimp stock, clam juice, tomatoes, remaining bay leaf and 1/2 teaspoon salt and bring to a simmer. Simmer, stirring occasionally, until slightly reduced, 12 to 14 minutes.

Add clams in even layer and gently simmer, covered, until clams just start to open, 4 to 5 minutes. Add cod, then shrimp, in even layers and gently simmer, covered, until just opaque throughout and clams have opened, 3 to 4 minutes more. Remove and discard bay leaf and any unopened clams. Serve cioppino in bowls, sprinkled with chopped parsley and fennel fronds and drizzled with oil, alongside lemon wedges and toasted bread.