Melt the butter in a large pan over a medium-low heat. Add the onion, celery and potato, cover and sweat for 6-8 minutes, stirring occasionally, until softened.
Add the stock to the pan, bring to the boil, then simmer, partially covered, for 20 minutes, or until the potatoes are tender. Set aside to cool slightly then blend, in batches if necessary, until smooth.
Return the soup to a clean pan and stir in the cream and most of the parsley (reserve some for garnishing). Season with black pepper and gently reheat until just simmering, but don't let it boil.
Ladle into warm bowls and crumble the Stilton over them. Serve sprinkled with the remaining parsley and freshly ground black pepper.
Cook's tip: Freeze after step 3 in individual portions for an instant homemade lunch that you can take to work, reheat until piping hot and enjoy.