PEANUT BUTTER-CHOCOLATE BARK TRIANGLES

Steps:

• Turn large baking sheet upside down. Cover tightly with foil. Mark 12x9-inch rectangle on foil. Stir bittersweet chocolate in medium metal bowl set over saucepan of barely simmering water (do not allow bottom of bowl to touch water) until mixture is melted and candy thermometer registers 115°F. Remove from over water. Spoon 2 tablespoons melted chocolate into small metal bowl; set aside. Pour remaining melted chocolate onto marked rectangle on foil. Using icing spatula, spread chocolate to fill rectangle. Refrigerate while making peanut butter filling.
• Stir chopped white chocolate and peanut butter constantly in heavy medium saucepan over medium-low heat until mixture is melted and smooth. Remove from heat. Mix in chopped nuts. Cool mixture to barely lukewarm, about 10 minutes. Pour over bittersweet chocolate. Working quickly, spread to coat bittersweet chocolate completely. Sprinkle with 3/4 cup chopped brittle. Chill until very firm, about 20 minutes.
• Stir milk chocolate in medium metal bowl set over saucepan of barely simmering water (do not allow bottom of bowl to touch water) until chocolate is melted and candy thermometer registers 115°F. Remove from over water. Pour chocolate over brittle, spreading quickly to cover. Sprinkle with 1 cup brittle. Rewarm reserved 2 tablespoons bittersweet chocolate over simmering water, stirring until warm. Dip spoon in chocolate and drizzle lines over brittle. Chill bark until firm enough to cut, about 20 minutes.
• Lift foil with bark onto work surface. Cut crosswise into 5 approximately 2-inch-wide strips. Cut each strip crosswise into 4 sections and diagonally into 2 triangles. (Can be made 2 weeks ahead. Chill in airtight container. Let stand at room temperature at least 30 minutes and up to 1 hour before serving.)