Preheat oven to 400 degrees F and preheat a slow cooker to low.
Line a large baking pan with parchment paper.
In a large bowl, combine ground meat, cheddar cheese, egg, onion, water, nutmeg, and allspice.
Roll the mixture into 1.5-inch meatballs and arrange them on the lined baking pan (may require two depending on how large your pan is — makes about 24 meatballs)
Bake for about 20 minutes or until a thermometer reads 140 degrees F.
Meanwhile, in a small skillet, heat the butter, chicken broth, and heavy cream over medium heat.
Once it begins to simmer, reduce the heat to low and let continue simmering for about 20 minutes until it reduces in half (stir frequently, especially toward the end).
Stir in the mustard and Worcestershire sauce.
Pour the sauce into a slow cooker and add the meatballs when they’re ready.
Cook on low for about 2 hours so the meatballs can marinate.
Stir every half hour or so, covering all the meatballs, and don’t cook in the slow cooker longer than two hours, or the sauce may start to separate.
That last instruction is key. If you don’t mix and cook too long, the cream in the sauce will begin to separate (yep, I cooked it for 4 hours once and it still tasted fine but was much less pleasant to look at after 4 hours! Live and learn!)