Finely shred the green cabbage and grate the carrots. Place both vegetables into a large mixing bowl.
In a separate bowl, whisk together the mayonnaise, sour cream, white vinegar, sugar, Dijon mustard, celery seed, onion powder, salt, and black pepper until smooth and creamy.
Pour the dressing over the cabbage and carrots. Toss gently until all the vegetables are evenly coated.
Cover the bowl with plastic wrap or transfer the coleslaw to an airtight container.
Refrigerate for at least 4 hours, or overnight for the best flavor and texture.
Remove the coleslaw from the refrigerator and stir gently to redistribute the dressing.
Taste and adjust the seasoning if needed with a little more vinegar, sugar, salt, or pepper.
Serve chilled with fried chicken, chicken tenders, burgers, barbecue, or sandwiches.