Heat the oil in a large saucepan. Add the onion and fry for a few minutes. Add the sweet potato and cook for 5 minutes, adding a splash of water if it starts to stick.
Meanwhile wash the kale and remove any hard stalks – these will not blend well.
Put the kale in the pan along with the vegetable stock, bring to the boil and allow to simmer for 10 minutes. The kale and sweet potatoes should be soft.
Add the nutmeg, remove from the heat and cool slightly and then blend to a purée using a stick-blender (or in a blender or food processor).
Return the soup to a clean pan and simmer over a medium heat. Pour in the milk and add black pepper.
In a separate pan, fry the bacon lardons and set aside.
To serve the soup, top with the bacon lardons and grated Parmesan.
