Preheat oven to 325℉. (Some ham packaging materials will suggests an oven temp of 275℉, but I've found that 325℉ works better).
Remove packaging from ham and double check the flat side for a bone protector (small plastic disc). If present, remove and discard.
1 8-12 pound spiral-sliced ham
Whisk glaze ingredients together in a small mixing bowl.
⅔ cup brown sugar, ⅓ cup honey dijon mustard, ¼ cup orange juice
Place ham in your roasting pan or baking dish. Brush with half of the brown sugar glaze. I like to temporarily lay ham on its side to work glaze between slices!
Arrange ham flat side down, cover tightly with foil and bake 10-20 minutes per pound. I start at 10 minutes per pound, then add more time as needed. Bake time varies greatly depending on ham size and shape (also a roasting pan will cook ham faster than a regular baking dish)!
When a meat thermometer registers an internal temperature of 130℉, remove from the oven and brush ham with remaining glaze.
Increase oven temp to 400℉. Bake ham an additional 10-15 minutes until it reaches an internal temp of 140℉ and glaze is sticky and caramelized. Watch closing to avoid burning.
Let your ham rest 15-20 minutes then serve! Thankfully a spiral ham is pre-sliced so you don't have to worry about carving or cutting it. Just tear slices away from the bone and enjoy.