Preheat the oven to 275 degrees F (135 degrees C).
Place the ham cut side down onto a sheet of aluminum foil. I like to put the shiny side up. Mix together the brown sugar, apricot jam and mustard powder in a small bowl. Brush onto the ham using a pastry or barbeque brush. Reserve any leftover glaze. Enclose the foil around the ham and place on a rimmed baking sheet.
Roast for 2 hours in the preheated oven, or if your ham is a different size, figure 14 minutes per pound. Apply the remaining glaze 20 minutes before the ham is done.