Preheat oven to 250°F. Spray a large roaster with cooking spray. Pour puff corn into the roaster.
Melt butter in a large saucepan over medium heat. Add brown sugar and corn syrup and mix well. Bring mixture to a boil, stirring constantly, and cook for additional 2 minutes.
Remove from heat and stir in baking soda and vanilla extract; the mixture will foam and expand. Carefully pour syrup over puff corn and toss to mix.
Bake for 45 minutes, stirring every 15 minutes. Pour onto waxed paper or foil that has been sprayed with cooking spray. Let Caramel Puff Corn cool at least 30 minutes. Break into bite size pieces and store in closed container.
Note: Puff corn is found in the snack/chip aisle of the grocery store.