Cut off and reserve some of the greener part of the leeks and thinly slice the white part. Melt the butter in a large saucepan and add the sliced white leeks. Sprinkle in a pinch of salt and cook gently for 5 minutes over a low heat until the leeks have softened.

Add the potatoes and pour in the stock. Bring to the boil and simmer for 5 minutes until the leeks are soft. Add the smoked haddock and cook for 5 minutes, by which time the potato should be al dente. Pour in the cream and add some white pepper. Continue to cook for a further 3–4 minutes, until the potatoes start to break down.

Meanwhile, take the reserved green part of the leeks and cut them in half lengthways and then into long, thin strips (like long matchsticks). Heat about 1cm (1/3 inch) of sunflower oil in a large frying pan over a high heat, add the leek strips, in batches, and fry for about 2 minutes until evenly golden and crispy. Remove with a slotted spoon and drain on some kitchen paper.

Divide the soup between warmed soup plates and serve with the crispy fried leeks scattered over the top and some wheaten bread on the side.