Either use a hand mixer or a manual masher and mash the celery root to your tast
Eat
Smile
Enjoy
Notes
Helpful tips
Use a heavy duty peeler because this root is tough and knobby.
Stick a fork into a piece at 30 minutes to test it, the same as you would for boiling potatoes. Keep checking the celery root in five-minute increments until it's as soft as you want it.
You can use either a hand masher as I did, or a hand mixer.
I can't give you the exact measurement of light cream. But you want to add only a little at a time, until you reach the consistency you prefer without making your mashed celery root too wet.