• In a medium bowl, sift together the flour, baking powder and salt. Set aside.
• Place chocolate in the top of a double boiler over steaming water. Stir until the chocolate has melted and set aside to cool.
• In a large bowl, beat with stand mixer or hand held mixer butter and sugar at medium speed until smooth, about 3 minutes. Add the two egg yolks and vanilla, beat at low speed just until blended.
• Add the dry ingredients and mix just until incorporated and dough is smooth. The longer you beat the dough, the softer it gets and becomes more difficult to handle.
• Divide the dough in half. Put one-half of the dough in a separate bowl and stir in the orange zest. The dough remaining in the mixing bowl, add the melted chocolate and cocoa powder. Mix with a wooden spoon or low-speed just until the chocolate has blended completely into the dough.
• Form each dough into a disc and wrap separately in plastic wrap or wax paper and refrigerate for about 45-60 minutes.
• Two options: pinwheels or checkerboards or both.

Pinwheel cookies:

• Remove dough from refrigerator. Take each dough disc and place between two sheets of wax paper and roll out into a rectangle to about 1/8 inch thickness.
• Remove the top piece of wax paper from each rectangle. Carefully, take the chocolate rectangle and flip onto the other dough rectangle. Trim the edges evenly and roll lengthwise. Gently press in the ends and trim evenly. The roll should be approximately 9 inches long.
  Wrap in plastic wrap and refrigerator for 1 hour or overnight.

Checkerboard cookies:

• Remove dough from refrigerator and cut each disc into 6 equal portions. Take each strip/portion and begin to roll in your hand and then continue on the counter with a little
  bit of flour to prevent dough from sticking. Roll out each approximately 9 inches long.
• Begin forming the checkerboard by placing each roll alternating each dough. At this time, slightly beat the egg white and lightly brush the top of each layer with your finger with the egg white. This will help each layer to glue together. Gently press the layers closely together to create a checkerboard pattern.
• Trim the end evenly. Wrap in plastic wrap and refrigerator for 1 hour or overnight
• Preheat oven to 350 °F. Line baking sheets with parchment paper.
• Using a sharp knife, cut either pinwheel or checkerboard log crosswise into 3/8 inch slices. Place 1-2 inch apart on the prepared baking sheets.
• Bake cookies about 8-12 minutes or just until the edges begin to turn lightly golden.
• Allow cookies to cool on wire racks. Store in an air tight container or freezer up to 2 months.