1. In a large bowl, dump in both bags of coleslaw mix. For a finer texture, pulse the coleslaw mix in a food processor a few times.
2. In a smaller bowl, combine the white sugar, milk, mayonnaise, buttermilk, Dijon mustard, apple cider vinegar, lemon juice, grated onion (or onion powder), salt, and black pepper. Whisk vigorously until thoroughly combined.
3. Pour the dressing over the coleslaw mix. Stir well to combine. Cover and refrigerate for about an hour before serving to let the flavors meld.
4. Stir again before serving. Enjoy this creamy coleslaw as a side dish or topping!