1. Generously butter a 13 by 9-inch shallow baking dish.
2. In a large saucepot, bring the bourbon to a boil over high heat. Boil until reduced to 2 tablespoons, about 2 minutes. Add the butter, reduce the heat to medium-low, and stir until melted. Add the marshmallows and stir until melted and smooth.
3. Add the cereal and pretzels. Stir gently until evenly coated. Immediately transfer to the prepared pan and press firmly into an even layer. Cool completely, then cut into 12 bars.