Line a rimmed baking sheet with parchment paper.
Reduce the puff right into a rectangle, ensuring all sides are trimmed, and place on ready pan. Rating a ½” border on both sides. Dock the middle by poking holes all by means of the middle rectangle inside the scored border. Refrigerate till able to assemble.
In a big sauté pan, prepare dinner the bacon over medium warmth. Cook dinner simply till among the fats is launched, 3 to five minutes. The bacon will end cooking within the oven. Take away the bacon from the pan and instantly add the onions. Cook dinner the onions within the bacon fats till softened, 2 to three minutes. Season with salt and pepper. Take away from warmth and mix with bacon.
To assemble: unfold crème fraîche evenly over dough. Sprinkle a good layer of the onion/bacon combination over the crème fraîche. Grate nutmeg evenly excessive. Chill the tart for half-hour.
Preheat oven to 375°F convection (400°F typical).
Bake till dough is puffed and appears dry, about 10 minutes. Scale back the temperature to 325°F convection (350°F typical). Bake till crust is a deep golden brown and the underside is evenly browned, 25 to half-hour. Let cool barely earlier than slicing and serving. Finest served heat.
