1) Chop potatoes into about 1/2 inch pieces and boil in salted water until tender, about 8-10 minutes.
2) Meanwhile, dice up red onion and celery.
3) Whisk together olive oil with mustard and honey.
4) When potatoes are done, drain well and add to bowl with other veggies. Pour in dressing and stir well to mix.
5) Add capers and season salad with salt and pepper.
6) Serve salad with fresh watercress.