Add the oil in a saucepan over a high heat, add the chopped vegetables and cook for 10 minutes.
Check and stir regularly.
Using a cheese grater, grate the zest off the orange into a small bowl.
Add the zest to the pan with the vegetables. Put the lid on and cook for 10 more minutes, stirring occasionally.
If you’d like to add wine now ‘s the time.
Add the stock or water and bring up to a simmer, then put the lid back on the pan and leave to simmer gently. After 45 minutes, test that the carrots are really soft by poking them with a knife or skewer. Turn off the heat. Carefully ladle the soup into a food processor or use a stick blender. Whizz the soup until it is smooth.
Cut the orange in half, squeeze the juice from one half and add to the soup.
Return the soup to the pan, heat it gently and season to taste.