Directions

Butter a 15 by 10-inch baking pan and line with parchment paper. Break white and bittersweet chocolate baking bars into 1-inch pieces. Do not mix together. In the top of a double boiler or in a heatproof bowl over barely simmering water, melt the white chocolate with the peanut butter, stirring occasionally until smooth. In a second double boiler or in a heatproof bowl over barely simmering water, melt the bittersweet chocolate, stirring occasionally until smooth.

Remove both mixtures from the heat. Pour the peanut butter mixture onto the prepared baking sheet, covering the entire surface of pan. Using a small spoon, drizzle bittersweet chocolate in straight lines over the spread mixture. Using the tip of a small knife, drag through the drizzled bittersweet chocolate to marbleize.

Chill in the refrigerator until firm, at least 2 hours. Cut into small pieces to serve. Keep chilled for up to 2 weeks.