Brush the inside of a baking dish with olive oil or butter, and slice your potatoes finely with a mandolin or with a sharp knife. Layer them in the baking dish with salt and pepper, onion slices, truffle slivers, and bits of previously sautéed bacon. Slice the Reblochon in half crosswise, and lay the cut sides down on top of the potato slices. Pour milk over the entire dish until it comes up at least halfway. Grate on a little nutmeg and bake in a slow oven until potatoes are tender and the Reblochon golden. Cover with foil if the cheese browns too quickly or if the dish is in danger of drying out, or add a bit more liquid to make sure the dish remains moist. Serve with a green salad, a crusty loaf of bread, and a fruity white wine. Note: White wine or broth can be used in place of milk.