This is great as is, though some carrot or beet would add some color (and extra nutrients).
3 T Dijon mustard
1 T red wine vinegar
3 T extra virgin olive oil
1/2 t dried dill, basil, tarragon or thyme…
1/4 t each salt and ground black pepper
3 c peeled and either cubed, shredded, or matchstick cut celeriac
1. Put the mustard in a medium bowl and whisk in the vinegar. Gradually whisk in the oil, slowly; don’t add it in all at once. Add the dried herb and season with the salt and pepper. Whisk again and toss in the celeriac, stirring to coat the celeriac with the dressing.