If using a clay baker, soak it in water for at least 15 minutes.
Preheat the oven to 350F.
Peel and cut onions into small wedges.
Peel, core and cut the apples into 1/2" cubes.
Heat oil in a skillet. Sprinkle the loin with salt and pepper. Sear the meat on all sides over fairly high heat, about 5 minutes per side or until golden brown. Remove the meat from the pan and set it aside.
In the same skillet, over high heat, quickly brown the onions for about 2-3 minutes, stirring every 15-20 seconds.
Spread the apples and onions on the bottom of the clay baker or Dutch oven. Place the pork loin on top. Crumble bouillon cube all over the meat and apple/onion mix. Pour in the cider and cover with a lid.
Braise in the preheated oven for 1 hour and 20 minutes. Do not open the oven until the time is up.
Carefully take the clay baker/Dutch oven out of the oven, place it on a cooling rack or on top of the stove, and let the dish rest for 10 minutes without opening it.
Transfer the roast to a large cutting board, slice into 1" - 1/25" slices and serve right away sprinkled with chopped parsley and topped with pot juices with onions and apples.