| 3 tablespoons | Cider vinegar |
| 2 tablespoons | Whole-grain mustard |
| 1 teaspoon | Kosher salt |
| | Freshly ground black pepper |
| 1/3 cup | Extra-virgin olive oil |
| 1/2 | Head Napa cabbage, thinly sliced, about 6 cups |
| 6 | Scallions (white and green parts), thinly sliced |
| 1 | Orange or yellow bell pepper, stemmed, seeded, and thinly sliced |
| 1 | Red apple |
| 2 cups | Watercress leaves |
Whisk the vinegar with the mustard, salt and pepper, to taste, in a large bowl. Gradually whisk in the olive oil, starting with a few drops and then adding the rest in a steady stream to make a smooth, slightly thick dressing. Add the cabbage, scallions, and bell pepper and toss until the vegetables are coated. Serve now or cover and refrigerate for up to 4 hours.
Before serving, grate the apple (with the skin but not the seeds) directly into the slaw, add the watercress leaves, and toss again. Season, to taste, with salt and pepper.