2 oz. butter
salt and black pepper
1 Tb cream (or 2 Tb milk)
Peel the celeriac and cut into rough chunks. Put into boiling salted water and simmer until soft (30 minutes approx). When soft drain it well and mash it roughly with a Potato masher (you don’t have to be too particular as a little texture in the mash is pleasant).
Beat in the butter and cream and season well. This reheats well.