In a medium saucepan, combine 1 ¼ cup apple cider, brown sugar, ½ tsp all-spice, nutmeg, and cinnamon sticks and bring to a boil. Once boiling, lower heat and let mixture simmer for 12-15 minutes, until mixture thickens a bit.
Pre-heat oven to 325 degrees.
Place ham in a baking dish, fat side up and pour ½ cup apple cider on the bottom of the pan. Brush about half the apple spice glaze over the ham, making sure to get it into the slices. Cover ham with foil.
Bake ham at 325 degrees for 15 minutes per pound of ham. If your ham weighs 10 pounds, you'll want to bake it for about 2.5 hours. When the ham has about 40 minutes left to bake, remove from the oven.
Place sliced apples in a bowl and toss with ½ tsp of all-spice and cinnamon.
Add apples and onions to the bottom of the pan and brush the rest of the glaze on the ham, once again making sure to get in between the slices. Place back in the oven, uncovered, and bake until the ham registers at 130 degrees and the apples are tender.