Place popcorn kernels in a medium to large sized brown paper bag, and turn under to close. Pop corn in a microwave for 3-4 minutes, or until popping slows or stops.
Add chopped apple pieces and nuts to popped corn in the bag.
In a mixing bowl, or large measuring cup, mix together brown sugar, butter (or coconut oil), corn syrup, salt, and vanilla. Stir well to combine.
Microwave butter sugar mixture for 1-2 minutes until boiling. Stir, and microwave again for 2 more minutes.
Immediately add baking soda to caramel and stir well. Caramel will foam.
Pour caramel over popcorn, nuts anda apple pieces in the bag, and turn bag over a few times to close. Shake well to distribute. Return the bag to the microwave for 1 more minute. Shake bag vigorously again and return to microwave for another 45-60 seconds.
Pour caramel apple corn out onto a baking sheet, break apart any large clumps, and let cool completely to harden.
Microwaves will vary, so keep a close eye on this as you are cooking. If corn does not crisp up, put it back in the bag and microwave for another 30-45 seconds. Best eaten the same day.