1 Heat a large saucepan. Add the butter and olive oil. Add the onion, garlic, leek and celery. Cook while stirring for at least 5 minutes or until golden and caramelised.
2 Add the kumara, stock and seasoning. Simmer for 30 minutes then puree until smooth.
3 To make the dumplings; preheat oven to 200C. Mix the flour, baking powder, salt and watercress together. Rub in the butter then mix in enough milk to make a soft, scone-like dough. Knead briefly then shape and bake for approximately 10 minutes or until golden.