Preheat oven to 250 degrees. Place butter, brown sugar, and corn syrup in a saucepan over medium heat and let come to boil for 5 minutes without stirring
Remove from heat and add baking soda and vanilla. This will foam up a bit.
Place bag of puffed corn in a large bowl and pour mixture over corn stirring well. *Puffed corn can be found at most grocery stores in the chip aisle. Get butter flavor...not cheddar. I used Seyfert's brand but do a Google image search for puffed corn to find other types.
Pour mixture over baking sheet and bake at 250 for one hour stirring every 15 minutes. When finished sprinkle lightly with sea salt. We have also added milk chocolate chips and nuts at the end of baking with good results.