Step 1

Heat the sunflower oil in a large pan and gently cook the onion with a big pinch of salt for 10 minutes, adding a splash of water if the onion starts to catch, until completely soft. Add the garlic, black pepper and thyme, and cook for a few minutes. Tip in the carrots and parsnips, and toss to coat in the oil, then pour in the stock, bring to the boil, then reduce to a simmer and cook for 20 minutes until the vegetables are soft.

Step 2

Pour in the double cream, if using, and use a stick blender to whizz the soup until completely smooth. Season and divide between four bowls, then add another drizzle of cream, if you like.