Recipe courtesy Emeril Lagasse, adapted from Essential Emeril: Favorite Recipes and Hard-Won Wisdom From My Life in the Kitchen, Oxmoor House, 2015, courtesy Martha Stewart Living Omnimedia, Inc.
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.