1. Melt the butter in a large saucepan. Add onion and cook for 2 to 3 minutes then stir in parsnip. Cover the pan and cook over a very low heat for 15 minutes.
2. Add the curry powder and cook for 2 to 3 minutes, then the orange zest, juice and chicken stock. Bring to the boil and simmer for 20 minutes.
3. Pour mixture into a blender and pulse until smooth. Reheat before serving and season to taste. Serve with orange zest.

Cook's tip: Make this the day before you serve it – soups and stews are always better the next day.