In a large bowl, measure 9 cups of Chex and set aside.
In a microwave safe bowl, combine chocolate chips, peanut butter, butter and vanilla. Microwave at 30 second intervals until almost melted then stir till smooth.
Pour the peanut butter mix over the cereal and stir until evenly coated.
In two ziploc bags, divide up the powdered sugar (¾ cup in each bag). Add the cereal, and shake