Heat the olive oil in a large, heavy-bottomed soup pot, add the onions, leeks, and celery, and saute until translucent, about 6 minutes. Add the garlic, tomatoes, saffron, and seasonings. Stir about 2 minutes, then add the white wine and cook 4 to 5 minutes, or until almost all the liquid has evaporated, before adding fish stock. Bring to a boil, then reduce to a simmer and cook 45 minutes. At the end of 45 minutes, add the potatoes and cook 20 minutes longer, or until the potatoes are tender.
Preheat the oven to 300 degrees.
While the broth is simmering, make the peppery croutons: Brush one side of each French bread slice with the olive oil, sprinkle with cracked pepper, and toast in the oven until crisp (about 12 minutes). After the potatoes have simmered 20 minutes, add the fish. Reheat to just below a boil and cook at a strong simmer 3 to 5 minutes, until the fish is cooked but not yet flaking apart. Remove the bay leaves, taste for seasoning, and serve immediately, garnished with the Peppery Croutons.