I'm in love with this recipe - it's perfect when I have some marshmallows left and they aren't fresh enough for s'mores. Typically I add in chocolate chips or pecans at the end (or both) and a bit of salt.
8 cups popcorn or 1 bag popcorn
1/2 cup butter
1 cup brown sugar
1 tablespoon light corn syrup
20 large marshmallows
Pop the popcorn and place it in a bowl - make sure that there are no un-popped kernels there.
Melt the butter in a medium pot on the stove. Add brown sugar and corn syrup and stir until well blended. Bring the mixture to a boil and boil for about 2 minutes. Add marshmallows and stir continuously on low heat until all melted. Add to the popcorn mixture and then sprinkle with chocolate chips, nuts or whatever else sounds good. You can shape them in to balls, or make them into bars - like rice crispy treats.