Pop all the popcorn. Remove all uncooked kernels. Place popcorn in a very large baking pans. You will probably have to use 2 pans. If you like the carmel heavier use less popcorn. Add nuts ect now!
Preheat oven to 250. In a small sauce pan on low-med heat cook brown sugar,butter,corn syrup. When it boils set timer for 5 mins stirring constantly. Turn off burner. Add vanilla and stir. Use rubber spatchula pour carmel over popcorn scrape pan, stir carmel into popcorn.
Cook in oven for 1 hour. Stir every 15 min scrape carmel from bottom of pan and combine with popcorn. Fully cool, store in Zip lock bags or air tight containers.