If you are popping your own popcorn do this first.
Place popcorn in large bowl.
Preheat oven to 250 degrees.
In a saucepan over medium high heat melt butter. Stir in brown sugar, corn syrup, salt and vanilla. Bring to a boil, stirring constantly. Then don't stir it for 3 minutes straight, letting it continue to boil.
Remove saucepan from heat and stir in baking soda.
Pour this hot caramel mixture over your popcorn, stirring to coat all kernels. You need to move slightly quick during this part as the caramel dries.
Prepare 2 large cookie sheets by spraying them with nonstick spray. Place popcorn on top trying to make it 1 layer.
Put in the oven for 1 hour, stirring it every 20 minutes.
Remove from oven and let cool completely. Break popcorn into pieces.
Put popcorn in bowl, add in TWIX Bites and shake to combine.