Cut the cod into four equal portions. Put the cod in a shallow ovenproof dish.
Combine the crème fraîche, a teaspoon of chives, butter and milk in a bowl and mix well. Pour the mixture over the cod.
Place the dish over medium‑low heat, cover and cook for 6 minutes, then turn the heat up to medium and cook for a further 6 minutes or until the sauce thickens and the fish is cooked through.
Season, to taste, with salt and pepper. Sprinkle with chopped chives.