Cotriade

Ingredients

• 2 onions, thinly sliced
• 800 g potatoes, peeled, sliced 1 cm thick
• 50 g salted butter (Breton)
• 1 bouquet garni, thyme, bay, parsley
• Fish — firm-fleshed (first into the pot)
• 400 g conger eel, cut into sections
• 300 g monkfish or gurnard, trimmed, cut into portions
• Fish — medium-fleshed (added 5 minutes later)
• 300 g pollack, whiting, or mackerel, cleaned, cut into portions
• Fish — delicate (final 3–4 minutes)
• 200 g sardines or small sole, whole or filleted
• For the broth course
• 4 slices stale pain de campagne, dense, day-old, rubbed with garlic
• 1 garlic clove, halved, for rubbing
• For the sorrel sauce
• 1 small handful sorrel, finely chopped
• 2 tbsp cider vinegar
• 4 tbsp broth from the pot, ladled out once fish is cooked
• 1–1.2 litres water or light fish stock, enough to just cover the potatoes

Method

1. 1
   Melt the salted butter in a deep, heavy pot over a medium flame. Add the thinly sliced onions and the bouquet garni. Soften without colouring until the onions are fully translucent and yielding — they should offer no resistance when pressed against the side of the pot.
2. 2
   Layer the sliced potatoes over the onions. Pour over water or light fish stock to just cover. Bring to a gentle simmer and cook for 15 minutes. The potatoes are ready for the next stage when a knife meets slight resistance at the centre — they must not be fully cooked, only nearly so.
3. 3
   Reduce the heat until the surface of the liquid trembles but does not boil; the target is 78–82°C. This step is where the dish lives or dies: a rolling boil will shatter the flesh, cloud the broth, and destroy the quiet clarity that defines cotriade. Lower the firm-fleshed fish — conger eel first for its gelatin, then monkfish or gurnard — into the liquid. Maintain the temperature with vigilance for 5 minutes. The broth should smell clean and oceanic, with the faint sweetness of the eel's gelatin beginning to enrich it.
4. 4
   Add the medium-fleshed fish (pollack, whiting, mackerel). Continue at the same sub-boil temperature for 5 minutes. The flesh should begin to turn opaque from the outside inward, just visible at the thickest point.
5. 5
   Add the delicate fish — sardines or small sole — for the final 3–4 minutes. They are done when the flesh has just lost its translucency and separates along its natural flake when pressed very gently with a fingertip.
6. 6
   Ladle several spoonfuls of hot broth into a small bowl. Stir in the cider vinegar and the finely chopped sorrel to make the accompanying sauce; it should be sharp enough to cut across the richness of the broth — taste and adjust the vinegar accordingly.
7. 7
   Rub the stale pain de campagne with the cut garlic clove and place one slice in each deep bowl. Ladle the broth generously over the bread and serve immediately as the first act. Then transfer the fish and potatoes to a separate warmed platter and bring to the table alongside the sorrel-vinegar sauce.