1/2medium green cabbagecored, quartered and thinly sliced
1/2small red cabbagecored, quartered and thinly sliced
1/2small red onionhalved lengthwise and cut crosswise into thin slices
1/2cupcrumbled blue cheese
In a small bowl, stir together the mayonnaise, buttermilk (or sour cream), vinegar, salt and pepper until well combined.
Add the cabbages and onions to a large bowl and toss to combine. Stir in 3/4 of the dressing and toss until coated. Add more dressing, if needed. Add the blue cheese and toss gently, trying not to break up the cheese crumbles too much. Cover and refrigerate for at least 30 minutes before serving.