Combine the rosemary, sage, garlic, and salt and pepper in a small bowl and rub it all over the pork. Place the pork on a large plate, cover with plastic wrap, and refrigerate for a few hours.
Place a medium heavy pan that will hold the roast somewhat snugly over medium heat and add the butter and oil. When the butter begins to foam, add the pork and cook, turning occasionally, until lightly golden on all sides, 10 to 12 minutes. (Keep your eyes on the butter so it doesn't burn and reduce the heat a bit if needed.)
Add 1 cup of the milk and stir to loosen the browned bits attached to the bottom of the pan. As soon as the milk comes to a boil, reduce the heat to low, partially cover the pan, and simmer until almost all the milk has evaporated, about 15 minutes. Add 1 more cup milk and continue cooking, basting and turning the meat a few times, until most of the milk has evaporated. Cook the pork in this manner, adding the milk 1/2 to 1 cup at a time, until it reads 160 degrees F on an instant-read thermometer, about 2 hours. (The pork can be cooked up to this point 1 hour or so ahead. In that case, cook only until it reaches 155 degrees F, because it will keep on cooking as it sits in the hot pan juices.)
Remove the lid and raise the heat to high. If no more milk is left in the pan, add 1/2 cup or so more. Cook, stirring and scraping the bottom of the pan to release the browned bits and turning the pork once or twice, until most of the milk has evaporated and the meat has a rich, golden brown color. Transfer the pork to a cutting board and let it rest for about 10 minutes while you finish the sauce.
Spoon off some of the fat from the pan. Add 1/3 cup water and stir quickly, over medium heat, scraping the bottom of the pan until only the brown glazed clusters of milk particles remain.
Cut the meat into 1/2-inch thick slices and serve topped with a bit of the pan juices.
Pork loin is generally prepared with two center-cut loins tied together, thus making them "double loin roasts." If one loin roast is used instead of the double, the cooking time will obviously be reduced by about half. Since the pork loin is a lean piece of meat, make sure not to trim away the fat attached to it, because it will add additional flavor.
Recipe courtesy of BIBA'S TASTE OF ITALY (Morrow, 2001) by Biba Caggiano