Broccoli Stem and Carrot Slaw

6 broccoli stems (save the tops for something else), peeled and julienned on a mandolin

4 carrots, peeled and julienned on a mandolin

3 celery ribs, julienned

1 red onion, julienned

1 Granny Smith apple, skin on, julienned

1/2 cup julienned cornichons

1 1/2 cups mayonnaise

1/4 cup Dijon mustard

1/4 cup cider vinegar

1 clove garlic, smashed and finely chopped

Kosher salt