Peel potatoes, then cut the larger ones in half and boil for 20 minutes.
Combine breadcrumbs with salt and pepper and place on a baking sheet. Cook for no more than 2 minutes, or long enough to brown them.
While the potatoes are cooking, sautee the onion until it turns a golden brown.
Mash potatoes by hand or run through a ricer.
Chop salmon into small pieces (about 1/4 inch chunks). Dice the capers.
Blend the potatoes with the cream cheese while the potatoes are still warm, then blend in the remaining ingredients. Roll mixture into 15 equal-sized balls; an ice cream scoop is a good way to do this.
Place egg in a small container with a tablespoon of water and whisk. Place breadcrumbs in another small container. Roll each ball in the egg, then in the breadcrumbs, and place on a baking sheet coated with cooking spray.
Bake for 10 minutes, then turn over and bake for another 10 minutes.