Ingredients

• 4 medium leeks (white and pale green parts only), chopped
• 1 large fennel bulb, stalks discarded, reserving fronds for garnish, and bulb chopped
• 3 medium carrots, chopped
• 2 large celery ribs, chopped
• 4 large garlic cloves, finely chopped
• 1/3 cup extra-virgin olive oil
• 1 tablespoon herbes de Provence
• 2 California or 4 Turkish bay leaves
• 1/4 teaspoon cayenne
• 1/8 teaspoon crumbled saffron threads
• 5 pounds whole whiting, perch, or cod (preferably with heads), cleaned and rinsed well
• 5 medium tomatoes, chopped (4 cups)
• 2 cups dry white wine
• 4 (3- by 1-inch) strips fresh orange zest
• 6 cups water
• 3 tablespoons tomato paste
• 1 baguette, cut into 3/4-inch-thick slices
• Equipment: a food mill fitted with medium disk
• Accompaniment: saffron rouille

Instructions

1. Wash leeks .
2. Cook leeks, fennel bulb, carrots, celery, and garlic in oil with herbes de Provence, bay leaves, cayenne, saffron, 1 tablespoon salt, and 1/2 teaspoon pepper in an 8-quart heavy pot over medium heat, stirring occasionally, until softened, about 10 minutes.
3. While vegetable mixture cooks, cut fish crosswise into 2- to 3-inch lengths.
4. Add tomatoes, wine, and zest to vegetable mixture and bring to a boil, then boil 30 seconds. Add fish, water, and tomato paste and simmer, uncovered, stirring occasionally, until fish completely falls apart, about 30 minutes.
5. Preheat oven to 350°F with rack in middle.
6. Arrange baguette slices in 1 layer on a baking sheet and bake until golden brown and thoroughly dried, about 20 minutes.
7. Force soup through food mill into a large heavy pot, discarding solids. Reheat soup over medium heat, stirring occasionally.
8. Mound rouille on croutons and put 1 in bottom of each soup bowl. Pour soup around croutons.