1. 12-24 hours before you are going to roast the ham, combine the salt with the orange zest, thyme leaves, and crushed red pepper flakes. Rub all over the ham, then place in a plastic bag and refrigerate.
2. When you are ready to roast the ham, remove it from the refrigerator and pre-heat the oven to 500 degrees F. In a small bowl, combine the orange juice, bourbon, and maple syrup.
3. Using a sharp knife, score entire surface of ham in a crosshatch pattern, cutting down just through skin to the flesh underneath. Place ham in a roasting pan skin side up and pour the juice mixture over the ham. Scatter the orange slices and the shallot or onion pieces around the ham and place the roasting pan in the oven. Cook for 20 minutes.
4. Remove the ham from the oven and baste with the pan juices. Reduce oven setting to 350 degrees F. Continue to baste the ham every 15 minutes or so and cook for another 45 minutes-55 minutes, until the very center of the ham reaches an internal temperature of 145-160 degrees, depending on your personal taste. (If you find the bottom of the pan looking very dry, you can add a little water or chicken/beef stock to moisten it, if you like.)
5. When ham is done, remove it from roasting pan, cover it loosely with foil, and allow it to rest for 20 to 30 minutes. Keep in mind that it will continue to cook a bit while resting so be sure not to overcook in the oven.
6. Carve ham into thick slices and serve with the pan juices spooned over.