Trim pork from excess fat and with a knife slit the pork in half, not cutting completely through the meat. Open and cover with a sheet of plastic wrap. With a meat pounder, flatten it to an even 1 ½ inch (2 cm) thickness. It will resemble a rectangle.
Season well with salt, pepper, sage and sprinkle with cognac.
In a medium size bowl, combine glaze ingredients. Transfer to a pan and bring to a boil for 20 minutes.
Cover the pork meat with blanched spinach leaves. Drain apricots and arrange them on top. Roll up pork loin and tie it with a string.
Bake in hot oven 200 °F (400 °C) for 1 hour. Remove from oven and allow to cool.
Cut in slices. If the pork is prepared the day before, keep refrigerated with the glaze.
Sauté onion with apple in butter. Once cooked add flour and stir. Add wine and sherry. Reduce. Add mustard, maple syrup and beef stock. Boil for a few minutes. Force sauce through a strainer if desired.
Optional: Before serving stir in ¼ cup cream.