Preheat oven to 200 degrees F. Line a jelly roll pan with parchment paper. Add popped popcorn and spread in an even layer.
Caramel: Melt butter in a large non-stick skillet over medium heat. Once melted, stir in brown sugar, corn syrup, and salt until smooth. Bring to a boil over medium heat, stirring occasionally. As soon as the caramel starts to gently boil, boil for 2 minutes, stirring constantly. Remove from the heat and stir in baking soda and vanilla
Drizzle caramel over popcorn. Toss gently with a spatula until the popcorn is evenly coated.
Bake at 200 degrees F for 45 minutes, stirring the popcorn every 15 minutes.
Store caramel corn in an airtight container at room temperature for to 2-3 weeks
Video
Notes
Popcorn: Pop your own plain kernels in the microwave in a brown paper bag, or with an air popper, or if you want a richer butter flavor, use a bag of movie theater microwave popcorn.To Pop Popcorn without a Popper: Add 1/4 cup popcorn kernels to a brown paper lunch bag and fold the top closed. Microwave for about two minutes, or until you hear the popping slowing down.