Remove the core and thinly slice the Green Cabbage into fine shreds; transfer to a large bowl.
Peel and coarsely grate the Carrot and add it to the bowl with the cabbage.
In a separate medium bowl, whisk together the Mayonnaise, Apple Cider Vinegar, Granulated Sugar, and Dijon Mustard until smooth.
Stir in the Celery Seed, then season the dressing with Kosher Salt and freshly ground Black Pepper; taste and adjust for balance between tang and sweetness.
Pour the dressing over the cabbage and carrot, then toss thoroughly until every shred is coated.
Cover and refrigerate for at least 30 minutes (up to a few hours) to let the flavors marry and the cabbage soften slightly.
Before serving, give the slaw a final toss and adjust seasoning if needed — add a pinch more salt, pepper, or a touch of sugar or vinegar to suit your taste.
