Using your preferred method for popping corn, pop the kernels with the oil and salt. 

Preheat a very large pot over medium heat. Transfer the popped corn into your preheated pot, and sprinkle in about 1/4 cup of sugar. Using a rubber spatula, stir the popcorn constantly until you notice the sugar starting to caramelize slightly. Sprinkle in another 1/4 cup of sugar, and continue the process. 

When you sprinkle in the final 1/4 cup of sugar, add in the cinnamon as well. Continue to stir and let the sugar caramelize until it has reached a medium caramel color. Immediately remove from heat and pour onto a large sheet pan to cool. Enjoy!