Instructions: In the bowl of an electric mixer fitted with the paddle attachment, combine butter, sugar, and salt. Beat on medium speed until light and fluffy, about 2 minutes. Add flour, and beat on low speed until dough forms around paddle.

Turn dough out onto work surface, and divide into thirds. Sprinkle cocoa powder over one piece. Gather dough together, and blend by pushing it away from you with the palm of your hand. Continue kneading the dough for 1 to 2 minutes until it is smooth and the cocoa is completely incorporated. (The process is messy and will take several minutes, but the dough will ultimately absorb the cocoa powder.) Shape each piece into a disk. Wrap in plastic wrap, and refrigerate until firm, about 1 hour.

Remove chilled dough from refrigerator. Set one blond disk aside. Divide remaining blond disk into four equal pieces. Divide chocolate disk into five equal pieces. Roll chocolate dough into five long, thin ropes (20 1/2 inches long and about 3/8-inch in diameter). Roll blond dough into four long, thin ropes (20 1/2 inches long and about 3/8-inch in diameter).

Arrange ropes in a checkerboard design. Lay one rope of chocolate dough lengthwise on work surface. Place a blond strip adjacent to chocolate, and push together gently so that they will adhere to each other. Repeat with a second chocolate strip. There will be a layer of three ropes of dough (chocolate/blond/chocolate). Brush top of layer with egg white. Repeat, alternating colors so that a blond strip is over chocolate strip, chocolate over blond, and blond over chocolate. To form third layer, repeat process, alternating colors. Press to form a square log.

Roll out reserved blonde dough to a 21 1/2-inch by 6-inch rectangle about 1/8-inch thick. Trim edges. Brush with egg white. Place checkerboard log in center of rectangle. Fold dough up and over log to completely encompass it. Press lightly to seal. Halve crosswise. Wrap in plastic wrap, and refrigerate until firm, about 1 hour.

Heat oven to 375 degrees. Line baking sheets with Silpats (French non-stick baking mats); set aside. Remove chilled log from refrigerator, and slice crosswise 1/4-inch thick. Place on prepared baking sheets about 1 1/2 inches apart. Bake until light golden brown, 10 to 15 minutes. Transfer to wire racks to cool.

This recipe yields about 6 dozen cookies.

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