Melt the butter in a large saucepan over a medium heat. Add the leeks to the pan, then cook for 3 mins until starting to soften. Add the carrots, honey, chilli (if using) and bay leaf, then cook for 2 mins.
Pour in the stock, bring to the boil, then simmer for 30 mins. Blend the soup in batches, return to a clean pan, then season to taste. When ready to serve, bring back to a simmer, then ladle into mugs. Add a swirl of soured cream or yogurt and serve with garlic bread or bacon butties.