Watercress and Celery Salad

Ingredients

3 large ribs celery, peeled top to bottom with a vegetable peeler, removing all fibrous strings
1/2 small red onion, thinly sliced
4 ounces (1 bag or 2 bunches) watercress, stems trimmed
1/4 cup fresh lemon juice
1 teaspoon Dijon mustard
1 teaspoon nonpareil capers (not salt-packed; do not drain)
1/2 cup extra-virgin olive oil
1/2 cup Parmigiano-Reggiano cheese shavings
2 ounces (about 20 slices) thinly sliced cacciatorini or Felino, Genoa, or hard salami, julienned
Sea salt and freshly ground black pepper

Using a mandoline, shave the celery paper thin.
Bring a medium pot of salted water to a boil. Fill a medium bowl with ice water. Blanch the celery for 30 seconds. Drain the celery in a colander and immediately transfer it to the ice water. As soon as the celery is cool, drain and transfer to paper towels to remove any excess water. Dry the bowl. Add the celery, onion, and watercress, and toss well.
In a small bowl, combine the lemon juice, mustard, and capers. Using a fork or whisk, stir until the mixture is homogenized. Slowly drizzle in the oil, constantly whisking until it thickens.
Pour the vinaigrette over the celery and watercress, and toss well. Add the cheese and salami, season to taste with salt and pepper, and toss again. Divide the salad among 4 cold salad plates, and serve immediately.