Place 7 to 9 pounds bone-in ham cut-side down in a 5 to 7-quart slow cooker. Pour 1/2 cup apple juice into the bottom of the slow cooker.
In a small bowl, whisk together 1/2 cup brown sugar, 2 tablespoons Dijon mustard, and 1/4 cup apple juice. The mixture will have the consistency of a runny paste.
Pour the glaze over the ham. If using a spiral ham, ensure glaze gets between the layers.
Cover and cook on low for 4-5 hours.
After 4-5 hours, or once the ham reaches an internal temperature of 145 degrees Fahrenheit, carefully remove it from the slow cooker. Allow the ham to rest for 10-15 minutes before slicing and serving.