Make the peanut butter caramel corn: Place plain/unsalted popcorn (air-popped or made on the stovetop) in a bowl, set aside. In a medium pot, melt the butter, brown sugar, granulated sugar, heavy scream, and sea salt until the sugars are dissolved and you have a smooth sauce. Stir in the peanut butter. Pour the peanut butter caramel sauce over the popcorn, tossing to coat. Pour the caramel corn onto a sheet of wax paper and allow it to set.