Start by measuring out your cereal into a very large mixing bowl. You want a bowl big enough to stir the cereal without crushing the pieces. Set this aside. In a separate gallon-sized resealable plastic bag, add the powdered sugar, pumpkin pie spice, and cinnamon. Seal the bag and shake it well to ensure the spices are evenly distributed throughout the sugar.

In a medium microwave-safe bowl, combine the white chocolate chips and the butter. Microwave on high for 30 seconds, then stir. Continue microwaving in 15-second intervals, stirring each time, until the mixture is completely smooth and melted. Be careful not to overheat the white chocolate, as it can seize easily. Once melted, stir in the vanilla extract until fully incorporated.

Pour the melted chocolate mixture over the cereal in the large bowl. Using a rubber spatula, gently fold the mixture together. Move from the bottom up to ensure every piece of cereal is coated in white chocolate. Work quickly but carefully to avoid breaking the cereal squares. Once the cereal looks wet and covered, it is time for the final step.

Transfer the chocolate-covered cereal into the plastic bag containing the spiced powdered sugar. Seal the bag tightly, leaving some air inside to allow the cereal to move freely. Shake the bag vigorously for about 30 to 60 seconds until all the pieces are white and well-coated. Spread the muddy buddies out on a sheet of parchment paper to cool and set completely before serving.