- Heat the butter in a large saucepan. Tip in the onion and cook until softened, about 5 minutes, stirring often. Add the cauliflower, potato, stock, milk and seasoning. Bring to the boil, then reduce the heat and leave to simmer for about 30 minutes until the cauliflower is soft and the potato almost collapsing.
- Blend in a food processor until you get a creamy, thick soup. Thin to desired consistency with a little more warm milk. Ladle into mugs or bowls, top with the cheese pieces and stir through before eating to allow the cheese to melt.