Preheat oven to 350 degrees F.
In a large mixing bowl, whisk together all ingredients except for the donut cubes and Butter Rum Sauce. Add the donut cubes and toss until they have absorbed as much of the liquid as possible. Pour the mixture into a casserole dish and bake for 1 hour. Serve with Butter Rum Sauce.
In a saucepan, melt the butter and gradually stir in the confectioners' sugar. Add rum and heat until bubbly.