Preheat oven to 250 degrees F. Place popcorn in a very large bowl. Set aside.
In a medium saucepan melt butter over medium heat. Stir in brown sugar, corn syrup and salt. Bring to a boil, stirring constantly. Boil without stirring 4-5 minutes, or until the mixture is a deep golden color. Remove from heat and carefully stir in baking soda and vanilla. The mixture will bubble.
Pour mixture over the popcorn in a thin stream. Stir to coat the popcorn. Place popcorn on a large baking sheet that has been lined with a Silpat baking mat or parchment paper. Bake for 45 minutes stirring every 15 minutes. Remove from oven and let cool completely.
When the popcorn is cool, break into pieces. Melt the chocolate chips in the microwave. Drizzle chocolate over the popcorn. Add the chopped Heath candy bars. Let the popcorn set until chocolate hardens. Store in an airtight container for up to one week.
Note-you can also stir in some peanuts or almonds.