1) Preheat oven to 180 degrees C.
2) In a large mixing bowl, whisk together all ingredients except for the doughnut cubes and butter rum sauce. Add the doughnut 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.Butter Rum Sauce:
1) In a saucepan, melt the butter and gradually stir in the icing sugar. Add rum and heat until bubbly. Pour over each serving of doughnut bread pudding.