Method

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.
Pour in the double cream/creme fraiche, and use a stick blender to whizz the soup until completely smooth.