Heat the olive oil and butter in a large saucepan. Add the onion and saute for 5 minutes over a medium heat.
Add the potato, coriander and cinnamon and stir fry for a minute, then add the carrots, stock, 1 tsp salt and 1/4 tsp white pepper. Bring to the boil, then reduce the heat and simmer for 20 minutes until the carrots have softened.
Blend the soup, then adjust the seasoning to your taste. Serve in warmed bowls.