Remove and discard the outer leaves of the cabbage, rinse under cool water, cut the cabbage into quarters, and thinly slice each quarter into 1/8-inch ribbons.

Peel the carrots and shred them using the large holes of a box grater or julienne peeler.

Combine the sliced cabbage and shredded carrots in a large mixing bowl and toss gently to mix.

In a small bowl, whisk together the mayonnaise, apple cider vinegar, sugar, Dijon mustard, kosher salt, black pepper, and celery seed until smooth and emulsified.

Pour three-quarters of the dressing over the vegetables, reserving the remainder, and toss thoroughly using your hands or a large spoon for about 1 minute to coat evenly.

If more dressing is desired, add the reserved dressing a little at a time until you reach your preferred creaminess.

Transfer the coleslaw to a serving bowl or airtight container and let it rest at room temperature for at least 10 minutes to allow flavors to meld.

Taste and adjust seasoning with additional salt, vinegar, or sugar as needed before serving.