Bring water to a boil in a large pot. Add potatoes. Cook until fork tender about 7 minutes. Drain potatoes, cut half. Smash half using the palm of your hand against a flat metal pancake turner on a cutting board.
In a large cast iron skillet over medium high heat, cook bacon until crispy. Remove and set aside.
In the same pan, with residual pan drippings, add onion and celery. Stir occasionally, sautéing about 5 minutes until soft. Remove and add potato halves, cut side down. Cook over medium high heat until browned and crisp, about 5 minutes.
Add salmon to warm through. Add back bacon, celery and onion. Toss to combine. Plate.
In a small bowl, mix together, horseradish, sour cream, and dill. Dollop around bowl with potatoes and salmon. Top with capers. Serve immediately.