Cut the butternut into large chunks. Peel and chop the onion and garlic. Cut the celery into pieces. If you like it spicy, add 1 red chilli. Cut the chilli in half lengthwise, remove the seeds and chop finely.
Sauté the onion, garlic and butternut in the oil in a large pan. Add 1 litre of water and the stock cube and bring to the boil. Leave to simmer on a low heat for about 15 minutes until well cooked.
Chop the parsley and add to the soup. Purée the soup with a hand blender or in a food processor and season with salt and pepper to taste.