Smooth peanut butter and two types of chocolate make up this version of the beloved peanut butter cup.
Coat a 9-by-12 1/2-inch rimmed baking sheet with cooking spray, and line with parchment, leaving an overhang on ends. Melt bittersweet 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.
Melt milk chocolate with peanut butter in a double boiler or a heatproof bowl set over a pan of simmering water, stirring. Drizzle chocolate-peanut butter mixture over bittersweet chocolate, and swirl with a skewer. Refrigerate until firm, about 1 hour. Break into pieces.