Peel and julienne celery root. Blanch for 1 minute in boiling water; drain. Rinse in cold water; drain well. Place in a large salad bowl; add celery and cheese. In a small bowl, combine the mayonnaise, mustard, lemon juice, salt, pepper and herbs. Spoon over celery root mixture; toss gently. Chill at least 1 hour.
Editor's Note: Celery root can be planted from seed in spring and is harvested in late fall, or it may be purchased at most grocery stores and farmer's markets.