Rich, aromatic rouille is a classic lily-gilding for French fish soups; this one has an extra something special: saffron. Even if you love saffron, though, don't be tempted to add any extra threads. This is just the right amount to really flatter, not dominate, the soup.
Cooks' notes:
·Instead of your own roasted peppers, you can use rinsed bottled roasted red peppers.
·Rouille can be made 2 days ahead and chilled, covered.