In a small bowl, whisk together sugars and cinnamon until well combined. Lay parchment paper on counter or work surface.
Melt shortening in a 3-qt. saucepan over medium-high heat. Add three popcorn kernels and cover.
Wait for all three kernels to pop, then add popcorn and shake to coat with oil. Immediately add sugar/cinnamon mixture and quickly stir to mix well.
Cover and let cook, leaving lid slightly ajar to allow steam to release. Shake the pot every few seconds, lifting from heat and holding lid in place, to prevent the sugar from burning. Continue until popped popcorn has filled the pan, about 5-8 minutes.
Immediately remove from heat, pour onto parchment paper, and sprinkle with sea salt, if desired.
Cool 2-3 minutes and serve warm.
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Notes
Sugar: You can substitute all white sugar or all brown sugar for the sugar in the recipe -- it will change the finished look and flavor of the kettle corn, but it'll still be delicious!Storage: This cinnamon kettle corn is best served immediately, but you can store in an airtight container or food storage bag once it's fully cooled.