Pour off fat from casserole, reduce heat to medium, and add the remaining 2 tbsp. of the butter. When butter melts, add half the sage leaves and fry for a few seconds. Slowly add milk and cream (**Hands well back, as it will spatter and steam!) Add lemon zest, season with a bit of salt and pepper, and bring to a simmer. Reduce heat to medium-low to low, partially cover pot with lid, and gently simmer for about 45 minutes to 1 hour, turning pork after 30 minutes. If liquid in pot gets too low, add a splash of warm water. Check meat for doneness starting at about 45-50 minutes of cooking time, with a meat thermometer. It is done when it reaches 145-150° F. Remove meat to a cutting board and tent with foil. Let rest.

Meanwhile, add the remaining sage leaves to the pot and using a wooden spoon, stir and scrape the bottom of the pan to loosen all the browned goodness at the bottom. As you do, the gravy will gradually become darker and thicker. If it gets too thick, add a bit more milk to thin. Taste and add salt and pepper, to taste.

After meat has rested 10 minutes or so, thinly slice and place on a serving patter. Spoon warm sauce over meat.