Place the smoked haddock fillets in a wide shallow pan. Pour in the milk and water so the fish is almost covered. Add the bay leaf and bring barely to a simmer over medium heat — do not boil (small bubbles around edge). Poach gently for 6–8 minutes until the fish flakes easily. Turn off the heat and leave the fish in the liquid to keep warm while you prepare the rest.

Sweat the vegetables

In a heavy-bottomed pot or saucepan, melt the butter over medium-low heat. Add the sliced leeks and chopped onion with a pinch of salt and sweat gently for 6–8 minutes until soft and translucent but not colored. Add the minced garlic and cook 30–45 seconds until fragrant.

Add potatoes and simmer

Add the diced potatoes to the pot with the leeks and onion. Carefully pour in the milk and poaching liquid through a sieve or by lifting the fish out and setting it aside (reserve the fish skin/bones if present for extra flavor, discard if inedible). Add the black pepper, white pepper (if using) and a little extra salt if needed. Bring to a gentle simmer and cook for 12–15 minutes until the potatoes are tender when pierced with a knife.

Flake the haddock and finish soup

While the potatoes finish cooking, remove any skin and bones from the haddock and flake the flesh into large pieces. Return the flaked fish to the pot for the last 2–3 minutes to warm through. Stir in the double cream and chopped parsley, heat gently (do not boil once cream is added). Adjust seasoning with salt and pepper to taste.

Serve

Ladle the Cullen Skink into warmed bowls. Sprinkle with the snipped chives and a little extra parsley if desired. Serve immediately with crusty bread or oatcakes.