"The secret of this tender honey-baked ham is slow cooking. I start it in a low temp oven around 6 p.m. the night before if used for breakfast. If used for dinner, it can be started later in the evening, turned off and restarted the next morning. Don't use a spiral-sliced ham because it will dry out."
Blend brown sugar, honey, molasses, orange juice, and mustard together in a saucepan over medium-low heat until thickened, about 45 minutes. Remove from heat. Let glaze sit until flavors blend, 8 hours to overnight.
Preheat oven to 225 degrees F (110 degrees C). Place ham in a roasting pan.
Bake in the preheated oven, checking occasionally, about 10 hours. If ham begins to darken at that point, cover with aluminum foil. Continue baking, about 2 hours more.
Increase oven temperature to 275 degrees F (135 degrees C). Bake, coating ham thoroughly with the glaze mixture every 30 minutes, about 2 hours more. Remove from the oven and let stand 15 to 20 minutes before slicing. Serve any remaining glaze with ham, if desired.