Preheat oven to 250 F. Pop the popcorn kernels in air popper. Place popcorn in a large oven safe bowl. (Note: I had to use my biggest and next biggest pyrex bowls and a 9x13 pan to fit it all. Just divide up the popcorn and caramel amongst the dishes as best you can.)
In a medium saucepan combine the butter, sugar, light corn syrup, and salt. Melt slowly over medium heat, stirring constantly. When mixture comes to a full boil, stir constantly to prevent burning for 5 minutes.
After caramel mixture boils for 5 minutes, remove from heat and add the baking soda. Mix in baking soda carefully as the mixture will expand when you add it. Pour caramel over popcorn and mix well to coat the popped kernels.
Place in glass oven-safe bowls or on parchment-lined baking sheets and cook the caramel corn for 1 hour, stirring every 15 minutes. Remove from oven and pour onto parchment-lined sheet trays immediately. Cool and enjoy!
Either yellow or white popcorn kernels will work great for this recipe. Air-popped popcorn will yield the best results.If you prefer you can use organic corn syrup. Be sure to stir every 15 minutes so each piece of caramel corn gets fully coated.