Layer popped popcorn, peanuts, pretzels, and nutter butter cookies in a large roasting pan.
Melt butter in saucepan, add brown sugar and corn syrup, stir continuously until caramel comes to a low boil. Stir in salt.
Let cook at a low boil for 3 minutes. Remove caramel from heat and stir in 1 heaping teaspoon of baking soda, watch the fun foaming action. Stir well, making sure baking soda is completely incorporated.
Pour caramel over top of the popcorn mixture, gently toss to combine.
Place pan in preheated oven for 15 minutes, remove from oven and gently turn caramel corn over in pan with a spatula scraping the caramel off bottom of pan on to the top of the mix. Pop back in to the oven for another 15 minuts.
Remove from oven spread out onto parchment paper or cookie sheets to cool.