Peel the celeriac and chop off any knobbly bits. If your celeriac is covered in mud you might prefer to do this in the sink. Cut into similar sized pieces.
Bring a large pan of water to the boil and cook the celeriac until soft.
When cooked drain and return to the pan. Add the butterbeans and the olive oil or spread and mash well. You won't get it completely smooth but it has a nice texture so don't worry too much.
When you're happy with the texture add the chopped parsley and mash in briefly.
Notes
Nutritional information is approximate and is intended as a guide only.