Add the Flora Buttery to a large saucepan along with the leeks and garlic, and sauté for a few minutes, until soft and fragrant.
Add the chopped carrots and potatoes to the pan, as well as the vegetable stock, thyme and plenty of black pepper. Don’t worry if the vegetables aren’t entirely submerged. Cover the pan, and bring to a gentle simmer. Stirring occasionally, cook for around 10 minutes, or until the vegetables are tender.
While the vegetables are simmering, dissolve the cornflour in the cold milk (I found this easiest using a whisk).
When the vegetables are soft, carefully transfer the mixture to a blender, and blend until smooth. Return the soup to the pan, and add the milk mixture. Stirring regularly, cook over a gentle heat for a few more minutes until the soup has thickened up to your desired consistency. Check the seasoning (I added a lot more black pepper!), and serve topped with fresh parsley if desired.