Place the 1 spiral-sliced ham in the basin of a slow cooker.
In a small saucepan, combine the ½ cup brown sugar, ½ cup honey, 2 tablespoons Dijon or spicy brown mustard, ¼ teaspoon ground cloves, 2 cloves garlic, and ¼ cup water over high heat. Heat until just warm enough to dissolve the sugar. Pour the mixture over the ham, making sure to separate the slices to let the glaze get between.
Cover the slow cooker tightly with the lid, or, if the ham is too large, make a tight cover with aluminum foil.
Cook on low for 3-4 hours, or high for 2-3—just until warmed through.
Preheat the broiler, transfer the ham to an oven-safe dish, and set aside. Pour the cooking liquid into a small saucepan. Heat cooking liquid on medium-high for 5-7 minutes, or until thick and bubbly. Brush onto ham, and broil for 4-5 minutes, removing to baste with additional glaze every minute or so.
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Notes
I've made this recipe with both boneless and bone-in hams, and I do prefer the flavor and moisture you get from a bone-in ham, but it's hard to beat the convenience of a boneless. It's really up to you, whichever you prefer.
The general recommendation for ham serving sizes is that you need about ½ pound of boneless ham per person, or ¾ pound bone-in ham per person. I have found that a boneless quarter ham (about three pounds), is plenty to serve my family of three for dinner, and still have plenty of yummy leftovers for next-day sandwiches.
For a ham that is bordering on too large for the Crock Pot, go ahead and double the glaze. The foil lid doesn't need to be air-tight, you're just looking to keep the heat in. I just kinda wedge it along the edges and then twist it together at the top. Like making the slow cooker a tin foil hat.