Heat ¼ c. olive oil in a large soup pot over high heat. When hot, add onion, leeks, garlic, carrots, celery, fennel, bay, thyme, and parsley. Saute until vegetables begin to soften, about 5 minutes.
Add white wine and fish frames, salt and pepper, and enough water to cover, about 10 cups more or less. Bring to simmer. Reduce flame and let simmer 1 hour, until fragrant and fish bones are softened.
Put through food mill and return to pot. Add potatoes and tomatoes and cook for ½ hour. Add saffron.
Before serving, add fish filets. Simmer gently. Stor even more gently—they will break up as you stir.
To make sauce: roast red peppers over an open flame, peel. Roast garlic in foil pouch in oven with a little olive oil until very soft, about 30 minutes. Place garlic, red peppers, salt, harissa to taste and olive oil to moisten in a blender and puree until smooth.
Serve soup with a dollop of sauce, or let people serve themselves.