In a large sauce pan melt butter over medium heat. Once butter has melted, stir in brown sugar and corn syrup. Increase heat to medium high and continue to stir until sugar has melted.
Once sugar has melted allow to come to a boil and boil for 5 minutes.
Remove from heat and add in salt, baking soda, vanilla extract and green food coloring.
Add in popcorn and toss until lightly coated. Transfer to a lined cookie or baking sheet and bake for 5 minutes. After 5 minutes toss popcorn around and bake for an additional 5 minutes. Continue this process 1 more time until popcorn is completely coated.
Transfer to a clean baking sheet lined with wax paper and allow to cool for 1 hour. Break up into pieces and serve!