Heat the oven to 300°F. Add the ham to a roasting pan with a rack, then add about 1 cup water to the bottom of the baking dish (or enough to create a thin layer coating the bottom). Roast for about 1 hour and 15 minutes, or until an instant-read thermometer reaches an internal temperature of 115°F.
Meanwhile, stir together the mustard and jam to create the glaze.
Once the ham has warmed through, remove from the oven and raise the heat to 375°F. Paint the ham with about 2/3 of the glaze. Cook for another 15 to 25 minutes, until the slices are crisped and the glaze is deeply browned. Remove from the oven and paint with the remaining glaze.
Emma was the food editor at Food52. She created the award-winning column, Big Little Recipes, and turned it into a cookbook in 2021. These days, she's a senior editor at Bon Appétit, leading digital cooking coverage. Say hello on Instagram at @emmalaperruque.