Spray or butter the inside of a casserole dish well. Preheat the oven to 350 degrees F. Place the chocolate covered raisins for the sauce into a medium sized bowl with the rum. Allow them to sit and soak for at least 45 minutes.
In a large bowl, whisk together the milks, chocolate covered raisins, sugar, vanilla, cinnamon, salt and eggs. Toss the bread into the bowl and gently mix to coat.
Dump the mixture into the prepared casserole dish and place on the middle rack in the oven. Bake for 1 hour.
After your raisins have sat for the desired amount of time, heat a heavy skillet over low heat. Add the heavy whipping cream to the skillet. Slowly stir in the rum soaked raisins, vanilla and cinnamon then allow to come to a simmer.
Simmer for 25 minutes over low heat. While waiting combine the water and the cornstarch and mix until completely combined. After the sauce has simmered for 25 minutes whisk in the cornstarch mixture. Continue to whisk until the sauce begins to thicken, about 10 minutes.
When the bread pudding is ready to come out, carefully remove it from the oven. Allow to sit for 10 minutes before serving. Top with the sauce and serve with vanilla ice cream (if desired.)