Using a mandolin (very carefully) shave fennel and celery into salad bowl.
Set aside and make vinaigrette.
In a small jar or bowl combine mustard, lemon juice, salt and pepper. If using a jar pour in oil and shake vigorously until well combined. If using a bowl pour in oil and using a fork whisk until well combined. Add dressing to fennel and celery. Coat the vegetables with dressing. Using a vegetable peeler shave strips of Parmesan cheese over the salad to taste. Serve.