Place 9 cups Chex Mix in a large bowl. Set aside.
Heat butter, peanut butter and white chocolate chips in a small pot on LOW, stirring constantly. Mix until all melted and well blended.
Add vanilla and stir well. Take off heat and pour over cereal. Toss so that most or all pieces are well coated.
Place 1½ cups powdered sugar in a large ziploc bag. Pour cereal into the bag and shake until all the pieces are coated with powdered sugar.
Place in a bowl until ready to serve.