Peel the potatoes and cut into large bite-size chunks of roughly equal size. Rinse them to remove any surface starch, then place them in a large pan with sufficient salted water to cover the potatoes. Bring the water to the boil then turn down the heat and cover the pan so that it continues to boil gently.
Cooking time can vary depending upon the type of potato and the texture. Generally, however, somewhere between 10-15 minutes is sufficient. When you think that the potatoes are close to being cooked, pierce one or two of them with a fork. If the fork penetrates easily with little resistance, the potatoes are cooked enough (they will cook a little more later). Remove the pan from the heat and drain off the water.
Meanwhile peel and chop the onion. Heat the fat in a frying-pan and gently fry the onion for about 10 minutes until it softens and becomes translucent. Add the lardons and cook for another 5 minutes.
Mix the potatoes, onion and bacon and place in a large ovenproof dish and season with salt and pepper. Cut the Reblochon in two horizontally so you end up with two large circles of cheese, each about ½"-1" (1cm-2.5cm) thick. Place the cheese halves, rind side up, on top of the potatoes and pour the wine over. Bake, uncovered, in a preheated moderate oven (Mk 4 - 350ºF - 180ºC) for 20 minutes.
Serve hot, either on its own or push the boat out and serve it with Filet Mignon with Sage and Rosemary (Tenderloin of Pork). You'll not regret it!