In small microwavable bowl, place 1/4 cup of the white chocolate chunks; set aside. In large microwavable bowl, microwave remaining white chocolate chunks and the chocolate chips on High 2 minutes, stirring every 30 seconds, until melted and smooth. If necessary, microwave 30 seconds longer. Stir in peanut butter and cashews. Spread mixture evenly over cooled baked crust. Refrigerate until chocolate is set, about 15 minutes.