Heat the oil in a saucepan, add the onion and fry gently for 5 minutes until soft and lightly coloured. Add the sherry, if using, and bring to the boil.

Add the sliced carrots and stock to the pan and season to taste.

Bring to the boil, stirring, then lower the heat, cover and simmer gently for 45 minutes until the carrots are very tender. Leave to cool.

Pass the soup through a sieve or puree in a blender. Pour the soup into a bowl, cover and refrigerate for at least 2 hours or overnight.

Just before serving, stir the orange zest and juice into the soup, then taste and adjust seasoning. Pour into 4 chilled individual soup bowls, sprinkle a little grated carrot on to each bowl and serve at once.