Rouille is a zesty garlic and red pepper sauce that is usually served with bouillabaisse. Here it's stirred into the stew at the last minute to thicken and flavor it, and additional rouille is spread on the croutons that garnish it.
The rich, earthy rosés of Provence like a Domaine Jean Bagnis l'Estandon Rosé go particularly well with shellfish stews.