Preheat oven to 325 degrees F.
In a stand mixer, add all the custard ingredients and blend until well combined. Set aside.
In a small saucepan add the Caramel Rum sauce ingredients and stir until combined. Simmer over medium low heat, until bubbles form around the edges, about 2-3 minutes, until mixture coats the back of a wooden spoon. Pour into a 10 inch pie dish, cake pan or 10 individual ramekins. Swirl around to cover bottom of dish. Let sauce cool just 1-2 minutes before pouring the custard mixture over the caramel sauce.
Place the pie dish into a larger roasting pan and place in the oven. Pour 2 cups of hot water on the bottom of the larger roasting pan so the hot water comes 1-2 inches up the sides of the pie dish.
Bake 1 hour or until a knife inserted near the center comes out clean. Cool to room temperature then refrigerate for two hours or overnight.
When ready to serve, loosen edges with a knife and invert onto a large plate. Enjoy or keep refrigerated until ready to serve.
Optional toppings: sugar free eggnog drizzled over the top of each slice and some dried cranberries for color.