Peel the celery root and cut it into 1/2-inch cubes. Add the cubed celery root to the boiling salted water and cook until tender, about 15 minutes. Drain.
Combine the rest of the ingredients and whisk or shake to make a dressing. Pour the dressing over the cooked celery root and toss. Refrigerate at least two hours before serving.
Celery root (also called celeriac) is sometimes hard to find. Try to get ones about the size of a large fist; smaller ones have too much waste, and bigger ones are often pithy. This vegetable is not worth eating raw.
NOTES: Cooked celery root in vinaigrette -- This salad has an intense celery flavor. The taste is so strong that it should be served only with other strongly flavored foods. It would overwhelm veal, but would go well with a lamb roast. Yield: Serves 6-8.