Is that safe, using a brown bag? I've seen warnings that anything other than a purpose-made microwave bag or other purpose-made container might pose a fire hazard (yes, I know about the diacetyl warnings, but plastic and borosilicate glass microwave poppers have been available for years)
That said, I Googled and came up with this link of recipes:
http://familystylefood.com/2007/04/p...and-fancy.html
Further Googling brings this:
http://cru.cahe.wsu.edu/CEPublicatio...11/em4711.html
Scroll down to the end and you see a warning against brown-bag popcorn popping