PLACE all the Pistou ingredients in a food processor and process until almost smooth. Set aside.

HEAT oil in a saucepan over medium heat and sauté onion until softened. Add sweet potato and cook for 5 minutes. Add stock, garlic and chili and simmer for 10 minutes or until sweet potato is tender.

STIR in milk, peanut butter and rocket, remove from heat. Allow to cool slightly then blend until smooth. Reheat and season to taste. Ladle soup into bowls and serve with a swirl of Pistou.