1Heat the butter in a large saucepan. Tip in the onion and cook until softened, about 5 mins, stirring often.
2Add the cauliflower, potato, stock, milk and seasoning. Bring to the boil, then reduce the heat and leave to simmer for about 30 mins until the cauliflower is soft and the potatoes too.
3Use hand liquidiser or food processor until you get a creamy, thick soup. Top up with more milk to thin a little if serving in mugs.
4When ready to serve, warm through, ladle into mugs or bowls and top with the cheese pieces, then stir through before eating.
5You can make croutons and put them on the top or the soup tastes nicely with fresh crusty bread.