Fry the onion in a little oil until it softens. Add the cumin and chilli and cook for a minute then add the carrot, sugar and stock and bring to a simmer. Cook for 10 minutes or until the carrot is very soft, then whizz in a blender. Add some more stock or water if the soup is too thick and reheat if you need to. Stir through the coriander, season well. Add a spoonful of crème fraîche to each bowl to serve, if you like.