Pat the pork dry with paper towels; combine the spice rub ingredients, then rub all over the pork. Let sit at room temperature as you preheat your oven to 225F.
Transfer the pork to an oven-friendly stainless steel or cast-iron skillet, then place in the oven and roast until the pork reaches an internal temperature of 135F, about 90 minutes. As the pork roasts, combine the glaze ingredients in a small saucepan; bring to a simmer over medium-low heat and simmer until dark and thickened, about 15 minutes. Set the glaze aside.
Remove the cooked pork and set on a cutting board to rest; loosely tent with tin foil. Increase the oven temperature to 500F. As the oven heats, place the skillet on the stovetop over medium heat, and add the lard, onion, and a few sprinkles of salt; sauté until the onions are softened and starting to caramelize, about 10 minutes. Add the apple slices and toss with onions, then place the pork and any accumulated juices on top, brush the pork liberally with two layers of the glaze.
Roast until the pork is very dark and crispy on the outside, about 5-10 minutes. Rest for 5 minutes then slice and serve with the apple and onion slices plus any remaining glaze.
