Get a small brown paper bag - lunch size will do nicely.
Put 1/4 to 1/3 cup plain old popping corn in the bag. Fold over the bag
opening to seal tightly yet leave plenty of space inside the bag.
Put the sealed paper bag in the microwave oven and microwave at the same
settings used for commercial bags of popcorn. You may need to experiment
with the timing.
The popcorn pops perfectly with no salt, oil, butter or grease. Of course, if you like those things on your popcorn, you can just add them on.
Trivia - While experimenting with radar and microwaves during World War II,
scientists used a paper bag filled with popcorn to see if microwaves could
cook food. It worked.