Melt butter, brown sugar. stir in marshmallows until melted and blended. Stir over popcorn to coat - I like using pre made salted popcorn so I use microwave or store bought pre made movie style popcorn. I have made it with regular pop corn from my air popper too. its all delicious - I just prefer the salty popcorn with the sweet caramel. This carmel corn can also be formed into balls (which I usually do).