Make glaze: To a small saucepan add the brown sugar, honey, mustard, orange juice, cornstarch, cloves and salt and whisk well. Bring to a boil while whisking often. Cook for about 5 minutes over medium heat. The glaze should have slightly thickened.
Slow cook ham: Place the ham in a large slow cooker (make sure the cooker is large enough so that you can put the lid on!) and our the glaze on top. Close the lid and cook on LOW for 4 to 6 hours or on HIGH for 2 to 3 hours. Baste the ham every hour with the glaze, if you can.
Serve: Check the ham to make sure the internal temperature has reached 140°F. Rest is on a chopping board for 10 minutes, then slice to serve. If the remaining glaze is too thin for your liking, place it in a small saucepan on the stove and whisk in a slurry of a couple of teaspoons cornstarch and 1-2 tablespoons cool water. Bring to a simmer and cook until thickened to your liking. Serve over the ham.
Ham: I do not recommend cooking a spiral ham in the crockpot, because they tend to dry out so much. Instead, I always use a precooked boneless ham that we slice ourselves after cooking.Honey: I prefer using a mild honey because it is the main flavor in the glaze and I have little kids who turn their nose up at strong earthy flavors. Make sure to use a honey you like, and I would avoid varieties on the bitter side because heat can increase those notes.Mustard: I used a smooth and mild Dijon mustard, but feel free to use whole grain mustard, yellow mustard... whatever you have on hand and enjoy the taste of.Orange Juice: I always make this with orange juice because it adds so much more flavor to the glaze vs water! If you don't like orange juice, you can try pineapple juice or even cranberry juice for a cranberry glaze.
Thickening the remaining glaze: If your glaze just doesn't thicken, try bringing it to a boil once (the cornstarch needs heat to work). If that doesn't do the trick, add another cornstarch slurry - the amount you need greatly depends on the amount of juices your ham releases during cooking.Resting the ham: This is important for a juicy ham. Make sure to set the ham on a chopping board with a ridge around, or at least place the chopping board on a surface where a little juice spillage is fine.
When I make this recipe in the oven instead, I cook the ham in a large Dutch oven (just follow the glaze recipe above, then place the ham and glaze in a Dutch oven and close the lid). Bake it at 325°F for 1 h 30 mins, or until the ham is cooked through (baste it every 15 minutes and check for the internal temperature). The Dutch oven lid will help to get a nice crust on top. Make sure to check it every 15 minutes though to keep the ham from overcooking or turning black at the top, depending on your exact size ham.
Place leftover ham and glaze in an airtight container in the fridge for 4-5 days. I reheat it in a pan on the stove with the lid closed, or use it diced up in casseroles and soups.