Optional: Salt the cabbage (not required, but it helps it stay crisp a little longer). Place 6 cups shredded cabbage in a colander, sprinkle with 1 tablespoon kosher salt, and toss to combine. Place the colander on a plate or in the sink and let the cabbage sit for 30 to 60 minutes. Squeeze as much moisture as you can from the cabbage with your hands (no need to rinse).
Whisk ⅓ cup apple cider vinegar, 1 tablespoon honey, 2 teaspoons Dijon mustard, 1 teaspoon celery seeds, ½ teaspoon kosher salt, and ¼ teaspoon black pepper together in a large bowl. While whisking constantly, slowly pour in ¼ cup extra-virgin olive oil and whisk until incorporated. Taste and whisk in up to 1 tablespoon more honey if desired.
Add the salted cabbage or 6 cups shredded cabbage, 2 peeled and grated medium carrots, and 4 thinly sliced medium scallions. Toss to coat. Taste and season with kosher salt and black pepper as needed.
