Preheat the oven to 400 degrees F.
Wash the potatoes and boil them until just tender, 10 to 15 minutes. Cut in half. Meanwhile, in a pan, cook the bacon until crispy. Drain the potatoes and place them in an oven-safe pan with the bacon, bacon fat, and rosemary sprigs. Season with salt and pepper.
Bake in the oven for about 20 to 25 minutes, remember to stir the pan once or twice so that the potatoes are evenly browned and the bacon fat completely coats the potatoes.