Quarter 1 cabbage core remove using chef's knife cutting board. Shred fine Cuisinart food processor blade 4 pulses. Shred 2 carrots 1 onion same blade quick bursts. Pyrex bowl dump all dry.
Pyrex bowl whisk 1 cup mayo 2 tbsp vinegar 2 tbsp sugar 1 tsp celery seed ½ tsp salt ¼ tsp pepper. Whisk 1 minute smooth thick no lumps trails off whisk.
Pour dressing over shreds Pyrex bowl. Toss spatula fold gentle 2 minutes all coated no dry spots. Taste adjust salt vinegar pinch.
Lid Pyrex bowl fridge 1 hour minimum melds flavors crisps. Scoop serve cold extra pepper top.