How to Make It
Preheat the oven to 450°. On a rimmed baking sheet, toss the potatoes with the oil. Season with salt and pepper and roast, cut side down, for 15 minutes. Using a spatula, turn the potatoes and roast them for about 15 minutes longer, or until golden and crisp. Drain the potatoes on paper towels.
Meanwhile, in a small bowl, blend the cràme fraîche with the dill, capers and horseradish; season with salt and pepper.
To assemble the crostini, top each potato half with a smoked salmon strip and a dollop of sauce. Arrange the crostini on a platter and serve.