Doesn't sound like it'd work but it does. And very well too. I came up with this recipe whilst craving bread pudding but not wanting to wait or faff about.
Put the butter into a large mug and microwave until melted. Add the milk (the amount you add is up to you really, I just like my bread pudding quite soggy) and the egg. Stir.
Add the spices and salt. Stir.
Break the cob/bread roll into small chunks and put into the mug. Stir and squish until you get a nice mush. Throw in your add-ins. Stir.
Bung in the microwave for 2 minutes or until cooked in the middle. Eat while still warm.