Place a large heavy-bottomed pot over medium heat then add oil and 1 kernel of uncooked popcorn. Allow the oil to heat until the kernel pops then remove popped kernel.
Add remaining popcorn kernels and allow it to cook in oil until it begins to sizzle and the first kernel pops. Immediately sprinkle sugar and salt over popcorn then give it a quick stir to dissolve sugar.
Cover pot and shake gently, constantly keeping the pot over the heat. The consistent movement will prevent the sugar from burning while evenly coating the popcorn in sugar and salt.
Once the popcorn begins popping rapidly, remove and return pot to the heat in 5-second intervals until the popping has slowed to about once every 2 seconds. (Do not overcook the popcorn, as the sugar will burn and ruin the batch. Un-popped kernels are inevitable so just know that you will need to stop cooking before they’re all popped.)
Remove pot from the heat then immediately transfer kettle corn to a large bowl.
Allow kettle corn to cool and become crispy. Sprinkle lightly with additional fine salt to taste if necessary.
Notes
Make sure to let the kettle corn rest for a few minutes after popping. It tastes best when the coating has cooled but the popcorn is still warm!