Preheat your oven to 375°F (190°C). Rub a baking dish with the cut side of a garlic clove and lightly butter it.
In a skillet over medium heat, cook the bacon until it starts to brown. Add the sliced onion and sauté until soft and golden, about 5–7 minutes.
Boil the sliced potatoes in salted water for about 10 minutes, until just tender but not falling apart. Drain and set aside.
Layer half of the potatoes in the prepared baking dish. Season lightly with salt and pepper. Spoon over half of the bacon and onion mixture. Repeat with remaining potatoes and bacon mixture. Pour over the wine and cream, if using.
Place the halved Reblochon cheese on top, rind side up, covering as much of the surface as possible.
Bake for 20–25 minutes, or until the cheese is melted, bubbling, and golden. Let sit for 5 minutes before serving.