Pour the wine, sugar and a glass of water into a saucepan. Simmer over low heat until you have a thick, glossy caramel. Strip the pork fillet of its fatty parts, even it out and salt it carefully, brushing with oil. Tie the fillet with kitchen twine, inserting the sage leaves. Season with pepper and grease the meat with oil again. Brown the meat in the pan and finish cooking in the oven at 170 degrees for 35 minutes. The meat should be left to rest for a few minutes. Peel and slice the potatoes and apples into 2 mm slices, then salt and oil them. Proceed by layering the mille-feuille alternating a layer of potatoes with one of apples in a baking dish. Bake covered with parchment paper and a weight at 180 degrees for 20 minutes. Divide the fillets into portions, cut the mille-feuille into rectangles and serve by spooning the wine reduction sauce over the meat.