Heat the butter in a deep saucepan over a medium heat until just starting to sizzle, then fry the cumin seeds until toasted and crackling.
Add the onion, leek, garlic, star anise, carrots and a pinch of salt. Stir to coat. Cover, reduce the heat to low and cook gently for 15-20 mins, stirring occasionally until the vegetables have softened in their own steam.
Pour over the stock and bring the mixture to a simmer, then continue to cook for 10 mins until the carrots are tender. Spoon 2 tbsp of the cream into a small dish and set aside, then pour the rest into the pan and bring back to the boil. Remove the star anise and use a hand blender to blitz the mixture until smooth and silky. Or, tip into a standard blender in batches and blitz before returning to the pan. For a really smooth soup, push through a sieve into a saucepan. At this stage, the soup can be cooled completely and chilled for up to three days or frozen for six months. Defrost fully before reheating. Reheat until piping hot over a low heat, then pour into bowls, drizzle with the reserved cream and scatter the extra cumin seeds on top. Serve with these cheese, cumin & onion seed cornbread muffins, if you like.