Heat the oil in a large saucepan, then gently soften the garlic without colouring. Tip in the swede, carrots and two-thirds of the thyme, then pour in the stock and milk. Bring to the boil, then simmer for 15 mins.
Ladle a third of the soup into a blender, whizz until smooth, then pour back into the pan along with the beans. Check for seasoning, then return to the heat and warm through. Serve sprinkled with the remaining thyme and some warm, crusty bread rolls.