Heavy cream is not sour cream. Double creme is not heavy cream.
Make stock with the tops.
I'm not going to offer any more advice. ;)
LOL ... It didn’t take you long to gauge the level of my culinary expertise. I could give you an even more accurate gauge than saying “a box of macaroni and cheese”, etc., but I think I will let your understanding rest where it is.
Do I gather reasonably correctly that you would make a soup type dish with the celeriac, or are you looking more for a “mashed potato” type concoction? I know that celeriac is long-lasting, so I don’t feel under time pressure to use this immediately.