1. For dressing, combine mayonnaise, sour cream, vinegar, celery seed, salt and black pepper in small bowl; whisk until blended. Set aside.
2. For slaw, combine in large mixing bowl cabbage, apple, celery and toasted almonds; toss to combine.
3. Pour dressing over slaw; gently mix until coated. Cover; refrigerate at least 1 hour or longer. To serve, spoon into salad bowls.