Line dutch oven with parchment paper or grease the inside with butter.
Lay the Nutter Butter cookies into the bottom of the dutch oven in a single layer. Pour sweetened condensed milk over the top of the cookies.
Add peanut butter in small dollops across the top. Dump brownie mix on top and spread out evenly.
Pour milk over the top of the brownie mix, as evenly as possible (do not stir). Then, place thin slices of butter across the top of the ingredients.
Cover and place dutch oven over 10 pieces of charcoal. Add approximately 20 pieces of charcoal to the top. (Number of coals for 12" dutch oven. Reduce if using a smaller dutch oven.)
Cook for approximately 30 minutes (cook time will vary) and remove from heat once the cake is cooked through. (After 25 minutes, check every 5 minutes to make sure the bottom doesn't burn.)
Top with vanilla ice cream or just scoop right out of the dutch oven to enjoy!