Pierce pork with a sharp knife, making several slits all over the top of the leg; place into a large bowl.
Combine 1 cup cider, onion, garlic, salt, and pepper in a blender; blend until smooth. Pour over pork. Cover with plastic wrap and marinate in the refrigerator, 6 hours to overnight.
Preheat oven to 350 degrees F (175 degrees C). Remove pork leg from the refrigerator and bring to room temperature.
Transfer pork leg to a roasting pan, reserving juices that have collected in the bowl. Mix pineapple juice into the bowl; pour over the pork. Insert almonds and prunes into the slits on top and in the center of the pork. Inject some of the remaining cider into the pork using a baster. Pour any remaining cider on top. Rub lard over the top of the pork and cover with pineapple slices. Cover the roasting pan with aluminum foil.
Bake in the preheated oven, basting every 30 minutes with pan juices, until an instant-read thermometer inserted into the center reads 145 degrees F (63 degrees C), 5 to 6 hours. Remove foil and bake until browned, about 30 minutes more. Remove from oven, cover with foil, and let sit for 10 minutes before carving.