Use an air popper to pop the popcorn kernels. Set the popcorn aside.
In a small saucepan, melt butter over medium heat. When butter starts to foam, swirl the skillet until butter turns golden brown and develops an amber color and gives off a nutty aroma, about 1-2 minutes. Set aside.
In a small bowl, combine the sugar and cinnamon. Stir until combined.
Drizzle brown butter over the popcorn and season with cinnamon sugar mixture, tossing occasionally, until all of the popcorn is coated. Serve.
Note: if you don't have an air popper you can pop the popcorn on the stove with oil.
