My OH made this on Wednesday night and has asked me twice since then if I have posted a review, so here is his review
The recipe was 2/3 potato and 1/3 celeriac, but as we wanted to taste the celeriac (to see if we liked it) my OH used half potato and half celeriac. The only other change to the recipe he made, was to use cheddar cheese instead of spreadable cheese (spreadable cheese isnt something we buy, as it sounds yuck and full of preservatives).
Neither of us had tasted celeriac before and didn't really know what it tasted like, but we enjoyed it . "This is delicious, if I do say so myself!" was my OH's comment
The recipe was easy to follow and the puree was lovely and smooth. I nice change from normal mashed potato. I'm sure my OH will make this again