Place the peppers into a very hot oven 240°C/475°F/Gas Mark 9 and roast until the skins are charred black. Place the peppers into a polythene bag and seal the top, leave for 10 minutes.
Take the peppers from the bag and remove the blackened skin. Cut in half and remove the seeds then cut the peppers into thin strips. Save any liquid from the inside of the peppers as this can be addded to the soup for extra flavour.
Add sufficient cold water to the soup mix to make a smooth paste, add remaining water and bring to the boil. Cover and simmer for 15 minutes.
Add peppers, juice and half the chopped basil, bring back to the boil for a few seconds. Add a swirl of single cream and serve.