1. Put the oil in a pan and set over medium–high heat. When hot, add the onion. Sauté for 4–5 minutes or until the onion is golden. Add the curry powder and stir for 10 seconds. Now add the tomatoes, carrots, potatoes, peas, salt and 1 litre (1¾ pints) water. Bring to the boil. Cover, turn the heat to low and simmer gently for 45 minutes.
2. Blend the soup in batches in a blender, then strain it through a coarse sieve. Make sure you collect all the pulp under the sieve. Return the soup to the pan. Add the cream and stir. Now add the stock, adjusting the amount according to the thickness of soup you want. Stir to mix well. Reheat the soup, if you want it hot, or cover and refrigerate if you want it cold. Garnish with the chopped chives to serve.