Shred 1 medium head of cabbage (about 4–5 cups)
Thinly slice 1 small red onion
In a large bowl, combine the cabbage and onion
In a separate bowl, whisk together 1 cup mayonnaise, 2 tbsp apple cider vinegar, 1–2 tbsp sugar (to taste), 1 tbsp Dijon mustard, 1/2 tsp salt, and 1/4 tsp black pepper
Pour the dressing over the cabbage mixture
Toss until evenly coated
Taste and adjust salt, pepper, sugar, or vinegar as needed
Cover and refrigerate at least 30 minutes (up to 24 hours)
Drain excess liquid if desired before serving
Optional: add 1 shredded carrot or 1/4 cup chopped celery
Optional: add 1/2 tsp celery seed or a pinch of paprika