Gather the ingredients. Preheat the oven to 325 degrees F (165 degrees C).

Place ham, cut-side down, into a large roasting pan. Press brown sugar evenly onto ham. Pour apple juice into the pan. Cover the pan with a lid or aluminum foil.

Bake in the preheated oven until ham is heated through, about 1 hour 20 minutes. An instant-read thermometer inserted into the center should read 145 degrees F (62 degrees C). Let ham rest for 10 minutes before transferring to a serving plate. Pour remaining pan juices into a saucepan.

Combine flour and milk in a jar with a lid; shake until mixture is blended.

Bring pan juices to a boil. Slowly whisk flour mixture into the saucepan and cook until gravy is thick, about 5 minutes.