Cereal gives this bark crunch. The two flavors (and shades) of chocolate yield a two-tone appearance.
Coat a 9-by-12 1/2-inch rimmed baking sheet withcooking spray, and line with parchment, leaving anoverhang on ends. Melt white chocolate in a double boiler or a heatproof bowl set over a pan of simmering water, stirring. Pour into baking sheet, and spread in an even layer. Refrigerate until firm, about 30 minutes.
Melt milk chocolate in a double boiler or a heatproofbowl set over a pan of simmering water, stirring. Mix in crisped rice cereal. Spread milk chocolate-cereal mixture over white chocolate. Refrigerate until firm, about 1 hour. Break into pieces.