We used a mug that we thought was pretty standard, but I think something with a little wider/shallower shape would work best--almost like a soup mug.
I was nervous when we had it in the microwave because it started overflowing, but it didn't get messy it just puffed up and stayed there. We have a pretty new and powerful microwave so we did it for 1 minute and 40 seconds. It was still gooey in the bottom, but any longer and it would have overcooked the top part...that's why I think a shallower-ish mug would be perfect!
Here's the part where you make the depressions:
Here is Erin enjoying a bite :)
Definitely a quick, good dessert for a hangering preggo.