Melt the butter in a large saucepan over medium heat. Add the marshmallows and cinnamon and stir until melted and smooth, 4 to 6 minutes. Remove from the heat and add the bourbon. Add the cereal in two parts. Fold to combine.
Spray a 9-by-13-inch baking pan and a nonstick spatula with cooking spray. Press the cereal mixture into the pan and press down using the prepared spatula. Let cool completely before cutting.