The method used to make this gives the best result for all vegetable-based soups. Use it for any combination you like, remembering that the potatoes or root vegetables you use are thickeners. If you are adding leaf vegetables just make sure there is a good proportion of denser crops to result in a smooth puree, you can always thin the soup with more stock at the end if it turns out to be too thick.
Serves 4
1 In a solid-based saucepan melt 1tbsp of butter into 2tbsp of olive oil.
2 Sweat off a finely chopped medium-sized onion.
3 Add 4 peeled chopped celery stalks and 2 medium-sized (mashing) potatoes, peeled and cubed.