In a medium bowl, whisk together the mayonnaise, apple cider vinegar, granulated sugar, celery seed, salt, and black pepper until well combined and smooth.
Taste and adjust seasoning if necessary. For a thinner dressing, add a teaspoon of milk or water.
Pour the dressing over your prepared coleslaw mix and toss to coat evenly.
Notes
This dressing is best served chilled. It can be made ahead of time and stored in the refrigerator for up to 5 days.