In a large glass bowl, whisk and combine the mayo, buttermilk, agave, celery seed, pepper, and lemon juice.
Add sliced cabbage and stir well to coat with the combined mixture. Refrigerate for several hours to let the flavors blend before serving.
Put your vintage kitchenware/cookware to good use.
Here is a way to produce your own wholesome Buttermilk full of beneficial probiotics.