My lovely (ex) mother-in-law inspired this idea. She would never dream of buying microwave popcorn, and had probably gotten sick of the mess and cleanup associated with making popcorn on the stove, so she started making her own microwave popcorn.
Her method is to use a paper sandwich bag (not waxed). Pour popcorn kernels into the bag until the bottom is about covered, toss in some butter if you want, and fold down the top of the bag 2 or 3 times. Then microwave it for 1-2 minutes or so until the popping slows to a few seconds between pops. Salt and eat!
I tried this and had pretty good luck with it. It sure is a whole lot cheaper than purchased microwave popcorn and the result has much fresher and better flavor as well. The biggest drawback is that it often burns badly before you can pull it out of the microwave. I tried pouring a little oil in the bag, but this made the burning worse.
I did some research online and the best result comes with adding nothing — no butter or oil — except some salt if desired, using a third of a cup of popcorn, and taping the bag closed with a piece of masking tape. Hardly ever burns unless you leave it in too long, pops up a nice full bag and tastes great with some melted butter (which you have earned by popping the corn without a single added calorie!)
Take that, Orville!