This is very quick and easy - and good with cod or other white fish.
Check the Good Fish Guide to see what's sustainable.
Serves 4.
Preheat oven to 200C.
Scatter the leeks over the bottom of an ovenproof casserole. Pour over the wine or stock, salt, pepper and mustard and mix together. Top with the fish and sprinkle with salt and pepper. Cover the casserole and put in the oven.
Bake for 10-15 minutes, or until a knife meets little or no resistance when inserted into the thickest part of the fish.
To serve, spoon the leeks and pan juices over the fish.
3 or 4 leeks, chopped and well rinsed
200ml dry white wine or chicken or fish stock
Salt and pepper
1 tbs Dijon mustard
500-750g cod fillets, about an inch thick