Place the Chex in a large bowl. Set aside.
In a small microwave safe bowl, add the chocolate chips, peanut butter and butter. Microwave in 30 second intervals, mixing until smooth. Stir in the vanilla.
Pour the chocolate mixture on top of the Chex cereal. Stir to coat.
Place the powdered sugar in a large ziplock bag until the Chex mixture is fully coated.
Line a baking sheet with parchment paper. Pour the Chex mixture on top and spread evenly. Allow the chocolate to harden. Store in an airtight container.