Roughly chop the washed celery including any leaves
To prepare the celeriac, take a large sharp knife and cut off the base and the top so it is stable on the chopping board. Use the knife to cut the thick skin off in strips working round the celeriac. Trim off any excess skin, wash and chop into rough pieces about the same size as the celery.
Add the celery and celeriac to a saucepan with the butter and cook over a medium heat until they soften slightly (about 5 minutes or so).
Pour over the chicken stock to cover the vegetables and bring to the boil.
Reduce the heat and simmer for about 15-20 minutes until the celeriac and celery are soft, but not overcooked.
Remove from the heat and allow to cool slightly.
Using an electric hand blender, blitz the soup until it is a smooth consistency. Be careful not to scald yourself.
Season with salt and pepper and taste, add more stock or a little water if the soup is too thick.
Serve with crusty rolls or french bread.
Recipe by The Kitchen Roebuck Park at https://www.jamespritchard.com/recipes/celery-celeriac-soup/