Preheat the oven to 250 degrees Fahrenheit and line two baking sheets with parchment paper.
Make your popcorn. Add your coconut oil to a large pan or dutch oven and melt over medium heat. Add 3 popcorn kernels and place the lid over the pan. Once they pop, the oil is ready. Add the remaining popcorn kernels, spreading out evenly over the bottom of the pan in a single layer. Cover with a lid and allow kernels to pop. Shake/agitate the pan around a few times while it pops to make sure all the kernels get popped. Once done, pick out any kernels that didn't pop (you can do this by transferring them to a bowl or baking sheet).
Next, make your caramel sauce. Melt your butter in a large saucepan over medium-low heat. I used the same pan as the popcorn cooked in and just wiped it out before adding the butter. Then add your coconut sugar and full-fat coconut milk and whisk well to combine. Cook for 5-7 minutes over a low simmer, whisking constantly. The sauce will thicken as it cooks. Remove from heat and let cool just a little (it will thicken a little more). Stir in the salt.
Add your popcorn to the saucepan the caramel sauce is in. Using a spatula, carefully mix well to combine, making sure to evenly coat all the pieces.
Spead the caramel popcorn out on the two baking sheets lined with parchment paper. The popcorn can be touching, but have it in a single layer. The more spread out it is, the crispier it will get. If there is extra caramel sauce in the pan, use a spatula to drizzle it over the popcorn.
Bake for 30-35 minutes at 250 degrees Fahrenheit, stirring once halfway through. Enjoy it warm or let cool completely before storing it! As it cools, it will crispy up more.