Roughly chop the onions and add to a large casserole dish with the olive oil. Sweat over a medium heat for a couple of minutes.

Chop the celery, discarding the tips and base, and add to the dish. Stir and cook for another 2 minutes.

Pour in the stock, cover and simmer for 10-15 minutes, until the celery is soft.

Turn off the heat and stir in the parsley. Blitz the soup with a food processor until smooth, then taste and season with salt and pepper.

To serve, drizzle each bowl of soup with a swirl of double cream. Yum!