In a glass microwavable bowl, combine the white chocolate chips, peanut butter, and butter. Stir to combine, and melt on high in the microwave for one minute. After one minute, stir the mixture, and microwave for 30 more seconds (or until mixture is smooth). Take out of the microwave and stir in the vanilla. Place the Chex mix in a large heat-resistant bowl & pour the hot mixture over top. Stir until evenly coated. Once covered, pour the mix into a 2-gallon resealable plastic bag or a large brown paper sack. Add the powdered sugar & shake until coated. Meanwhile, place the Cadbury Mini Eggs into a 1-gallon resealable bag. Crush with heavy object (rolling pin), until broken. Do not crush to crumbs. Mix the small chunks of Cadbury eggs into the puppy chow mixture.