Melt the butter in a pan, add the carrots and onion and cook for 10 minutes, without browning.
Add the stock, sugar, and salt and pepper to taste.
Bring to the boil, cover and simmer for 30 minutes or until the carrots are tender.
Sieve or work in an electric blender until smooth.
Pour into a soup tureen and stir in the orange rind and juice.
Leave to cool, then chill for several hours.
Just before serving, stir in the cream.