While your oven preheats to 320°F (160°C), combine the orange marmalade, light brown sugar, whole-grain mustard, red wine vinegar, ground allspice, ground coriander, and black pepper in a bowl, stirring until smooth and well combined. The mustard and vinegar will create a balanced acidity that cuts through the richness of the ham. Set this glaze aside. Score the top of your ham with shallow crosshatch cuts about ¼-inch deep, spacing them roughly 1 inch apart—this allows the glaze to penetrate and caramelize into the meat, creating a beautiful textured crust.

Place the scored ham cut-side down on a rack in a roasting pan and pour 2 cups of water into the pan around the ham—the water creates steam that keeps the meat moist during the initial cooking phase. Cover the pan tightly with aluminum foil and place it in the preheated 320°F oven for 1 hour. After 1 hour, carefully remove the foil (watch for hot steam), check that there's still liquid in the pan, and add a splash more water if needed. Return the ham to the oven, uncovered, for another hour until the meat becomes tender.

Remove the ham from the oven and increase the oven temperature to 400°F (200°C). Carefully pour off 1/4 cup of the flavorful pan juices into a small bowl and whisk them into the prepared glaze from Step 1. This addition of savory, ham-infused liquid deepens the glaze's complexity and helps it adhere better to the meat. I like to taste this enriched glaze and adjust the seasoning with a pinch more black pepper if needed—it should taste bold and balanced.

Using a pastry brush, generously coat the top and sides of the ham with half of the amplified glaze from Step 3, working it into the scored lines. Return the ham to the 400°F oven and roast for 45 minutes. Brush with the remaining glaze after 25 minutes and again at 40 minutes, allowing each layer to caramelize slightly before adding the next. The higher heat creates a glossy, deeply browned exterior while the sugar and fruit in the glaze develop rich caramelized notes.

Remove the ham from the oven and transfer it to a cutting board or serving platter. Let it rest for 15 minutes—this allows the juices to redistribute throughout the meat, ensuring each slice stays moist and tender. The glaze will also set slightly, creating a more structured crust. Carve and serve warm, spooning any pan drippings over the sliced ham for extra flavor.