Line a large baking sheet or plate with wax paper, parchment paper or paper towels. Set aside.
In a large bowl, measure cereal and set aside. In another smaller bowl, measure cinnamon sugar, set aside.
Melt butter. Pour over cereal and stir until all cereal is completely covered. Microwave for 2 minutes, stirring after 1 minute. Add cinnamon sugar one half at a time stirring extremely well between each addition. Microwave whole mixture again for 1 minute. Pour on to prepared lined sheet and spread out to cool.
Store in an airtight container for up to 5 days.