1/2 cup well-shaken buttermilk
2 tablespoons mayonnaise
2 tablespoons cider vinegar
2 tablespoons minced shallot
1 tablespoon sugar
1/2 teaspoon salt
1/4 teaspoon pepper
3 tablespoons finely chopped chives
1 pound Napa cabbage, cored and thinly sliced crosswise (4 cups)
6 radishes, diced
2 celery ribs, thinly sliced diagonally (optional)
Whisk together buttermilk, mayonnaise, vinegar, shallot, sugar, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a large bowl until sugar has dissolved, then whisk in chives.
Toss cabbage, radishes, and celery with dressing.
Optional: add some blue cheese, or put the dressing over an everything-but-the-kitchen-sink mixed salad.