Pat the ham dry with paper towels and place on a cutting board, cut side-down.
Score the ham in a criss-cross pattern using a small, sharp knife to cut about ¼-inch deep.
Coat the bottom of a roasting pan with the olive oil.
Place the ham cut side-down in the roasting pan.
Transfer the ham to the bottom rack of the oven and roast, uncovered, for about 2 hours. Baste the ham occasionally with any juices that have accumulated on the bottom of the pan.
While the ham is roasting, whisk together syrup, miso paste, mustard, sake, rosemary, lemon zest, garlic powder, and black pepper in a medium bowl to make the maple-miso glaze.
Remove the ham from the oven and increase the oven temperature to 400 F.
Brush the maple-miso glaze all over the surface of the ham.
Return the ham to the oven and roast for an additional 20 minutes, until the glaze is browned and the internal temperature reaches 140 F.
Allow the ham to rest for 10 minutes in the roasting pan.
Transfer the ham to a serving platter or cutting board and strain the pan drippings and liquid through a fine mesh strainer into a saucepan.
Use a ladle to skim fat from the surface of the drippings and discard.
Bring the sauce to a simmer and cook until slightly thickened, about 5 minutes.
Transfer the sauce to a gravy boat and serve with the ham.