There is very little that divides opinion more than celery and celeriac. You either love them or hate them. It’s interesting because their sisters (carrots and parsnips) are universally liked.
Saute one head of celery, two onions and a potato in 50g butter. Add one litre of stock and simmer until the celery is really tender. Mash 60g blue cheese to a cream and whisk slowly into the soup (low heat) just before serving. Add chopped parsley.