Microwave Christmas Pudding

In a nutshell, the microwaves impact the molecules of different molecules differently, depending on their polarity. Water molecules are polarized, and the microwaves make them spin crazy. As a result, the water is able to escape for the starch chains binding your baked goods together, rather than sticking to them as they would with ordinary heating. This applies to all sorts of baked goods, not just Christmas pudding, but breads and rolls as well.

I don't know the science behind it, but I find that starchy items, like bread, tortillas, etc., will harden upon cooling after being heated in the microwave. I think you have to be really careful not to over-heat it. I found this: https://www.quora.com/Cooking-science-why-does-bread-get-soft-then-rubbery-then-hard-after-being-microwaved