Preheat oven to 400°F Toss potatoes, olive oil, and rosemary in large bowl to coat. Sprinkle with salt and pepper; toss again.
Coat large rimmed baking sheet with nonstick spray. Transfer potatoes, cut side down, to prepared sheet. Roast until brown on bottom, about 15 minutes. Using metal spatula, turn potatoes over and roast until tender, 5 to 10 minutes longer. DO AHEAD Can be made 4 hours ahead. Let stand on sheet at room temperature. Rewarm in 400°F oven 5 minutes before continuing.
Cook bacon in medium skillet over medium heat until crisp. Using slotted spoon, transfer to paper towels to drain.
Place potatoes, cut side up, on platter (slice off rounded end to make flat, if necessary). Top each with dollop of crème fraîche, then bacon and chopped chives. Serve warm or at room temperature.