Method
You can make the court-bouillon immediately before poaching, or a day or two in advance (keep it stored in an airtight container in the fridge). Place all the ingredients except the fish into a large pan and cover with about 2 litres (3½ pints) water. Place the pan over a high heat and bring the contents up to a gentle simmer. Cook, simmering, for 25–30 minutes. Remove the pan from the heat and allow the stock to cool with all the vegetables and herbs in it.
Strain the stock through a sieve into a fish kettle. (Retain the vegetables as a lovely soup base – pop them in a bag and freeze them until you need them.) At this point you could add a few more aromatics, such as bay, if you like, but it’s optional. Place the fish kettle over a medium heat and bring it up to a simmer. Place the fish on the trivet (the kettle insert) and lower it very gently into the poaching liquid. Turn down the heat to low and cook the fish for 15–20 minutes, or until the fish is just cooked through. I sometimes test this by pulling gently at the dorsal fin. If it comes away easily, the fish is cooked.
Lift the trivet from the kettle and remove the fish to a large serving platter, then allow it to cool a little. You can bring the fish to the table whole, or you can cut it up and serve it in portions. Serve with buttered brown bread, good mayonnaise, and a watercress salad.