Prepare vegetables: core and finely shred green and red cabbage (use a sharp knife, mandoline, or food processor). Place shredded cabbage in a large mixing bowl.

Peel and grate the carrot and add to the bowl with the cabbage. Thinly slice green onion and add to the mixture. Toss to distribute evenly.

Creamy Dressing (Extra-rich)

Make the dressing

In a medium bowl, whisk together mayonnaise and sour cream until smooth. Add buttermilk, apple cider vinegar, Dijon mustard and honey; whisk until combined and slightly airy.

Season the dressing with celery seed, kosher salt and black pepper. Taste and adjust: add more vinegar for tang, more honey for sweetness, or an extra tablespoon of buttermilk to thin if needed.

Crunch & Brighteners

If using apple, core and julienne half a small apple and toss with lemon juice to prevent browning.

Toast sunflower seeds in a small dry skillet over medium heat, shaking frequently, until lightly browned and fragrant (about 2–3 minutes). Remove from heat to cool.

Chop parsley finely and set aside.

Assemble

Pour about three quarters of the dressing over the prepared cabbage mixture. Reserve remaining dressing for serving or to adjust creaminess later.

Add the julienned apple (if using), toasted sunflower seeds and chopped parsley to the bowl. Toss everything thoroughly so the dressing coats the vegetables evenly. Taste and add more dressing, salt, or pepper as desired.

Let the slaw rest in the refrigerator for at least 20 minutes to allow flavors to meld (up to 2 hours). Stir again before serving and sprinkle remaining seeds and a small pinch of parsley on top for garnish.