Heat oil and seasonings in cast iron casserole dish and when sizzling, add onion. Let soften for a few minutes and lightly brown, then add garlic.
Add sweet potato and vegetable broth, bring to boil and let simmer for about 10 minutes with a lid on casserole dish.
Then add the watercress and cook for a further 5 minutes or until sweet potato is soft when pierced with a fork.
Puree in food processor.
1 tbsp extra virgin olive oil seasoned with freshly ground pepper
Pinch of celery salt
Pinch of cayenne pepper
Pinch of turmeric
1 medium onion - finely chopped
2 cloves of garlic - grated
1 medium sweet potato - peeled and cut into small cubes
3 cups vegetable broth
4 oz watercress