In a small bowl, whisk the mayo, apple cider vinegar, mustard, sugar, salt, and pepper.
Add the cabbage and carrots in a very large mixing bowl, the larger the better. Pour the dressing all over the cabbage, and toss well to combine. Finish with salt & pepper to taste.
Serve right away, or let the coleslaw rest in the fridge for at least 30 minutes before serving.
Store leftovers in the refrigerator in an airtight container for up to 5 days, but it’s best within 3 days.
