3 tablespoons unsalted butter
1/3 cup granulated sugar
1/2 cup popcorn kernels
1/2 teaspoon salt
Melt butter in a large pot over medium-low heat (not a dutch oven). When butter has slowly melted for a while, skim solids off the top of butter and discard. Increase heat to medium.
Stir in sugar and popcorn until well combined. Cover, and cook popcorn until it's done popping, shaking the pot often (about every 20 seconds). Transfer kettle corn to a large bowl. Sprinkle salt and cinnamon over the top, and stir until well combined.