1Pop the popcorn. Pour into a bowl. Set aside.
In a large saucepan heat the butter over medium-low heat until melted; add the brown sugar and let cook for only 30 seconds,stirring continuously. (The sugar won't be dissolved -that the way it should look- cooking longer will crystallize the sugar.
2Add the marshmallows and stir until melted and combined;stir in vanilla, blend in.
Pour over the popped corn and gently stir to coat all. Great warm good cold too -stays soft. Can form into balls or leave loose. Or can add in extras like M&M's, sprinkles, other candy bites, bacon, etc...