In a small bowl, combine the mayonnaise, sour cream, sugar, apple cider vinegar, Dijon mustard, celery seeds, onion powder, and black pepper.
Add the coleslaw mix to a large bowl. Add ¾ of the dressing and toss to combine. Taste and add more dressing if you like it more creamy.
Serve immediately or refrigerate for one hour to allow the cabbage to soften. Personally, I think coleslaw tastes the best when it's still crunchy, so I eat it immediately.
Notes
Coleslaw mix: If you'd rather make your own, just combine 5 cups shredded green cabbage, 1 cup purple cabbage, and 1 cup carrots. You'll need about 8 cups of shredded vegetables for this recipe.