Finely shred the 1 small green cabbage cored and finely shredded (and ¼ small red cabbage cored and finely shredded if using) using a knife, mandoline, or food processor. You want thin, uniform strips about 1/8-inch wide. Place the shredded 1 small green cabbage cored and finely shredded in a mixing bowl.

Add the grated medium carrots peeled and grated or julienned and sliced green onions (if using) to the mixing bowl with the 1 small green cabbage cored and finely shredded.

Sprinkle 1 tsp of kosher salt over the vegetables and toss well. Let sit for 10 minutes — this draws out excess moisture so your coleslaw stays creamy, not watery. After 10 minutes, use your hands or a clean kitchen towel to squeeze out as much liquid as possible from the 1 small green cabbage cored and finely shredded. Discard the liquid.

In a separate mixing bowl, whisk together the ¾ cup mayonnaise, 2 tbsp apple cider vinegar, 1 tbsp Dijon mustard, 2 tbsp granulated sugar, 1 tsp celery seed, ½ tsp onion powder, 1 tsp kosher salt, and ¼ tsp black pepper until completely smooth and well combined. Taste and adjust — add more 2 tbsp apple cider vinegar for tang, more 2 tbsp granulated sugar for sweetness, or more 1 tsp kosher salt as needed.

Pour the dressing over the drained small green cabbage cored and finely shredded mixture and toss thoroughly until every strand is evenly coated.

Cover the mixing bowl tightly with plastic wrap and refrigerate for at least 1 hour before serving — this is key. The rest time lets the flavors meld and the 1 small green cabbage cored and finely shredded soften just slightly while staying crisp. For best results, refrigerate for 2–4 hours.

Before serving, give the coleslaw a good toss and taste for seasoning. Adjust 1 tsp kosher salt, ¼ tsp black pepper, or a splash more 2 tbsp apple cider vinegar if needed. Serve cold, straight from the refrigerator.