In a large bowl, whisk the mayonnaise, sour cream, mustard and vinegar. In a dry skillet over medium heat, toast the caraway and mustard seeds until fragrant, 2 to 3 minutes. Add to the dressing, season with salt and pepper and stir well.
Add the green and red cabbage, onion and carrots and mix well, massaging in the dressing to coat the slaw and tenderize the vegetables. Cover and set aside at least 10 to 15 minutes or refrigerate up to 2 days.
Photograph from "Guy on Fire: 130 Recipes for Adventures in Outdoor Cooking"