Skate with Black Butter

• 1 medium skate (ray) wing, 560–675 g
• 1 onion, sliced
• few sprigs

Choose a pan wide enough for the skate to lie flat while cooking. Put the skate in, cover completely with cold water, add the onion, parsley, salt and wine vinegar. Bring to the boil gently, cover and barely simmer for 15–20 minutes. If the flesh lifts easily from the cartilage the skate is cooked. Turn off the heat and transfer the fish on to a large serving plate. Skin and lift the flesh on t