However, we did several trials, so here are some photos from our earlier attempts. And yes, the scale did go up in the last few days...
We only got only hot spot with this one ... and the paper plate started to burn (note lower right corner).
We tried multiple bars to get broader coverage. This worked a little better.
A dish full of chips provided the best coverage of all, but was too hard to pinpoint the hot spots. After several minutes of microwaving, we got one fused, hard point of chocolate (indicated by spoon) but not a second spot to measure.
Best holder: glass baking dish
Best stand (to cover the rotating thing in the microwave): small plate
Best chocolate: Valentine's Day cherry cordials
This experiment has also been done with marshmallows and by kids on YouTube.