In a dutch oven, heat coconut oil until hot. (Test by putting one kernel in, and should bubble around the edges.) Add popcorn and swirl to coat.
Cover and cook on medium high, shaking pot, until all popcorn is popped. While doing this, occasionally let a little peep of air out so that popcorn doesn't steam. You can also use an air popper to make the popcorn if you'd like!
Put popcorn in a large bowl or pan, and remove any unpopped kernels. Add nuts, if using.
In a high sided saucepan, add maple syrup and butter. Boil until mixture reaches 230 to 235 degrees F on a thermometer. Remove and add salt, cinnamon, and baking soda, stirring. Quickly pour mixture on popcorn and stir to fully coat.
Pour mixture onto a parchment lined baking sheet in a single layer. Bake at 250 degrees F for 45-50 minutes, stirring once in the middle of baking, until mostly dry. Let cool completely; caramel corn will firm up and be perfectly crisp. Store in an airtight container or ziploc bag.