Step 1In a medium, heavy-bottom pot heated over medium-high heat, add the oil, then stir in the onions, leeks, garlic, parsley, bay leaf, oregano, thyme, pepper and saffron. Cook, stirring frequently, until the onion is translucent and the herbs are fragrant, 6 to 8 minutes.
Step 2Stir in the tomatoes, tomato sauce and wine. Cover and simmer gently to develop the flavors, 30 to 45 minutes. Thin if desired with 1/2 cup to 1 cup clam juice. Season with 2 teaspoons salt and 1 tablespoon hot sauce, or to taste. The cioppino base can be made ahead of time to this point; remove from heat, cover and refrigerate up to one day (reheat before continuing).
Step 3To the pot, add the shrimp, scallops and fish. Cover and simmer gently just until the fish and shellfish are firm and opaque, about 10 minutes. Uncover the pot and remove from heat. Stir in the chopped cold butter, stirring just until the butter melts to add a little richness to the broth. This makes about 5 cups cioppino. Ladle the cioppino into wide bowls, garnishing each serving with freshly chopped basil and oregano. Serve immediately.