2 Tablespoons olive oil
1 onion, thinly sliced
1 fennel bulb, core removed and thinly sliced
4 garlic cloves, minced
1 teaspoon red pepper flakes
1/4 cup tomato paste
1 cup white wine
1 28-oz can crushed tomatoes
1 1/2 cups clam juice
3 cups water or chicken broth
1 1/2 pounds firm white fish (such as cod)
1 1/2 pounds shrimp, shelled and deveined
Heat olive oil in enamel covered Dutch oven over medium high heat. Saute onions and fennel until softened. Add anchovies and break up with a spoon. Add red pepper flakes and garlic and stir until fragrant. Stir in tomato paste and cook until bubbly.
Add white wine, cook until reduced by half. Stir in tomatoes, clam juice and water and bring to a simmer. Cook undisturbed for an hour or so. Broth will reduce somewhat; if it becomes too thick just add water.
Cioppino can be made ahead until this point.
Lay fish in bottom of pan, add clams on top. Cover and cook until clams are nearly open, 10-15 minutes. Layer in scallops, mussels, and shrimp. Cover and cook just until mussels and clams are open, 5 minutes.
Ladle into large bowls, serve with toasted sourdough bread.