1. Line a rimmed 15- by 10-inch baking sheet with 6 ounces bittersweet chocolate foil; refrigerate.
2. Melt chocolates with salt and cinnamon in a large heat-safe bowl set over simmering water, stirring often. Stir in cereal and half of pistachios and cherries. Immediately pour onto prepared baking sheet and spread with a spatula into a large rectangle, about 1/4-inch thick. Sprinkle with remaining pistachios and cherries; drizzle with white chocolate.
2. Refrigerate until firm, about 30 minutes. To serve, break into pieces. To store, transfer to an airtight container and refrigerate up to 3 days.