Line a sheet pan with parchment paper. Melt white chocolate chips in a microwave and pour into the pan; spread into a rectangle about 1/4-inch thick and freeze 10 minutes. Melt semisweet chocolate chips. Spread over the white chocolate so that the edges are even. Sprinkle with 1/4 cup crushed starlight peppermints and 1/3 cup mini marshmallows. Refrigerate until firm, about 30 minutes. Pull off parchment and break into pieces. Makes about 24 pieces.