1. Remove the ham from the packaging, and if it’s a bone-in one, remove the cap that covers the bone.
2. Combine the mustard, brown sugar, vinegar, and honey in a bowl and spread it all over the ham. Then, drop it in the slow cooker, with the flat side down,
3. Cover and cook on LOW for four to six hours, or until it reaches 140F on a meat thermometer. You can also baste it with the pot juice or flip it halfway through the time.
4. Once the internal doneness is reached, take the ham out and tent it with foil. Then, let it sit and strain the juice from the slow cooker into a saucepan.
5. Cook the sauce at medium heat until it reaches a simmer. Then, whisk slurry from the cornstarch and water, and whisk it into the ham juice. Stir for one or two minutes until it reaches the desired thickness.
6. Serve the ham in slices, with the sauce on top.

Another way to monitor cooking time for ham can be watched here.