Celery root is pretty easy to prepare, but does discolor a bit once sliced open and grated. So make the dressing before slicing and grating the celery root, for best results. I like mine really mustardy, so I use a fairly large amount. If you’re unsure, start with less; you can add more, to taste, when the salad is finished. To peel celery root, lop off the root and opposite end with a chef’s knife. Then stand the round root on a flat end then take the knife and cut downward, working around the outside, to slice off the tough skin. In the states, celery root are often smaller, and have more complicated roots, and you’ll need to cut a bit deeper to remove them.