In a saucepan heat the olive oil until shimmering, then add the onion and garlic and sauté over medium heat for 3–6 minutes until the onion is transparent. Add the carrots, orange zest and stock, bring to the boil then simmer for 30 minutes. Remove from the heat, transfer to a blender and purée until smooth. Return the soup to the saucepan and add the butter and cream. Bring back to the boil and simmer for 3 minutes. Season with salt and white pepper to your taste. Divide equally among 6 soup bowls, add a teaspoon of crème fraîche to each serve, top with orange zest and a pinch of salt and sprinkle with chopped chives.