Preheat oven to 450°.
Coat the bottom of a large Dutch oven (or any other heavy oven-safe pot) with 1 tablespoon oil and add the sliced apples and onions. Sprinkle with a pinch of salt and pepper.
Cover the loin with the herbs and garlic, and a drizzle of the remaining oil.
Bake in oven for 15 minutes, uncovered. Then reduce heat to 350° and bake for approximately 60–75 minutes. Keep an eye on the onions and apples, adding ¼ cup of cider when needed to prevent burning.
Remove pot from oven when temperature reads 150°–155°. Remove pork from pot and cover with foil (temperature will rise another 5°–10° while resting for 10 minutes).
Place pot with apples and onions over a medium-low flame, stir in remaining apple cider to remove all the caramelized bits from the bottom of the pot. Allow to cool for 1–2 minutes, pour into a food processor and blend to a smooth consistency, adding water or cider if needed.
Slice the rested pork and serve with the apple gravy. Enjoy!