Napa Cabbage Salad with Buttermilk dressing

1/2 cup well shaken buttermilk
2 tablespoon mayonnaise
2 tablespoons cider vinegar
2 tablespoons minced shallot
1 tablespoon sugar
3 tablespoons finely chopped chives
1 pound Napa cabbage , cored and thinly slicedcrosswise (4 cups)
6 radishes, diced
2 celery ribs, thinly sliced diagonally

Wisk together buttermilk, mayonnaise, vinegar, shallot, sugar, 1/2 teaspoon salt and 1/4 teaspoon pepper in a large bowl until sugar has dissolved, then wisk in chives. Toss cabbage, radishes, celery with dressing