I have never understood the popularity of cod, other than as fish and chips. To me, it is a rather bland, uninspiring fish. So, when a cod recipe has me searching for superlatives, I know it must be something special. This is one such recipe from the manically brilliant Mr. Blumenthal. (Fear not, this one is actually pretty conventional.)
Rinse the sliced potato under running water for ~30 seconds then drain well.
Melt the butter in a saucepan over gentle medium heat and cook the onion and potato for 10 minutes, stirring frequently. Toss in the leeks and cook for 5 minutes more. Pour in the fish stock together with the bouquet garni, bring to a simmer and cook for 5 minutes (or until the potatoes are tender). Add the cream and milk and cook very gently for another 10 minutes.
To finish the sauce, remove the bouquet garni, blitz and strain into a clean pan. Season with salt & pepper and keep warm while you cook the fish.
Heat the oil in a fying pan on high heat. Season the fish with a little salt and sear it for about 2 minutes on both sides. The precise time will depend on thickness – you want it just cooked, only just “setting” in the centre.
Get all chefy and serve the cod on or surrounded by the sauce, sprinkled with chives and garnished with the pea tops. It goes well with some waxy potatoes (which could sit under the fish) and green beans.