In a large bowl, toss cabbage and carrot with the salt until well combined. Let sit for 15 minutes, then transfer to a colander and rinse thoroughly under cold running water. Spin the slaw dry in a salad spinner, or transfer it to a baking sheet lined with paper towels or clean kitchen towels and blot dry with more paper towels or a clean kitchen towel.
Rinse and dry the bowl, then add heavy cream and sugar and whisk until sugar is dissolved. Slowly whisk in vinegar; the dressing will thicken slightly. Whisk in mustard, white pepper, and celery seed.
Add cabbage and carrots to the dressing and toss to coat. Season with salt to taste, if needed. Cover, transfer to the refrigerator, and let sit at least 2 hours and up to 24 hours before serving.
