- ½ medium green cabbage, cored and thinly shredded (about 3 cups)
- ½ medium red cabbage, cored and thinly shredded (about 3 cups)
- ½ red onion, halved and thinly sliced
- 2 tablespoons plus ½ teaspoon kosher salt
- 4 tablespoons cider vinegar
- 3 tablespoons sugar
- 2 tablespoons Creole mustard, or other whole-grain spicy mustard
- ¼ teaspoon celery seeds
- ¼ teaspoon freshly ground black pepper
- 1/3 cup vegetable oil
- 4 green onions, minced
Toss the cabbage and the onion with 2 tablespoons of the salt in a large colander and set aside over another bowl or in the sink until the vegetables have wilted, about 1 hour. Rinse the cabbage mixture thoroughly under cool running water and then spin it dry in a salad spinner.
While the cabbage is wilting, make the dressing: Whisk the vinegar, sugar, mustard, celery seeds, pepper, and remaining ½ teaspoon kosher salt together in a small nonreactive mixing bowl. Little by little, add the oil in a slow, steady stream to form a smooth, slightly thickened dressing.
When you are ready to serve, toss the drained, wilted cabbage mixture with the green onions and enough of the dressing to coat the slaw. Taste and adjust the seasoning if necessary.