Step 1 Chop the onion and garlic finely and chop the pumpkin into evenly sized chunks of about 10cm. Dice the potato.
Step 2 Heat the oil in a large pot over a moderate heat. Add the onion, garlic and potato and cook until the onion is soft but not coloured.
Step 3 Add the pumpkin, stock and spices and bring to the boil, then reduce the heat and simmer for about half an hour, until the pumpkin is tender.
Step 4 Take the soup off the heat. Using a hand-held blender, blend the soup until smooth. Or using a regular blender, blend half the soup at a time and tip back into the pot. (If you don't have a blender, you could mash the pumpkin with a masher, or push it through a sieve with a spoon.)
Step 5 Serve with a dollop of sour cream and parsley or coriander sprigs.
Step 6 Serve with toasted tortillas or bread (gluten-free options are available).