Place toasted hazelnuts in your food processor along with the cocoa powder and process until the hazelnuts are finely ground. Set aside.
Preheat oven to 350 degrees F
In a small bowl whisk together the flour and salt. Set aside.
With a hand mixer, beat the butter and sugar until light and fluffy. Add the egg, vanilla extract and orange zest and beat until well blended. Add the flour mixture and beat just until incorporated.
Divide the dough in half and place one half of the dough back into the bowl of your electric mixer.
Divide the dough in half and place one half of the dough back into the bowl and add the cocoa and hazelnut mixture to the dough and beat until incorporated. Set aside.
Lay out two large sheets of parchment paper (about 10 x 12 inch) and on one sheet of parchment roll out the white dough into a 6 1/2 inch by 10 1/2 inch rectangle, making sure both sides of the dough are smooth. Wrap dough and place on a baking sheet in the freezer for about 15 minutes or until dough is firm.
Meanwhile, take the chocolate dough and remove 1/2 cup and cover with plastic wrap. Set aside.
On the second sheet of parchment roll out the remaining chocolate dough into a 6 1/2 inch by 10 1/2 inch rectangle, making sure both sides of the dough are smooth. Wrap dough and place on a baking sheet in the freezer for about 15 minutes or until dough is firm.
When both the white and chocolate dough are firm, remove from freezer and lay the white dough on a cutting board, removing the parchment paper.
Lightly brush the top of the white dough with a little water
Remove the parchment paper from the chocolate dough and place it evenly on top of the white dough.
Trim the edges of the two dough’s so the rectangle now measures 6 inches by 10 inches.
Take the chocolate dough trimmings and add to the 1/2 cup of reserved chocolate dough.
Lengthwise cut the rectangle into thirds (3 - 2 inch by 10 inch stripes)
Place one strip on a piece of plastic wrap. Brush the top of the dough with water and place the second strip on top of the first (alternate colors so you have white, black, white, black pattern). Brush the top of the second layer with water and stack the third layer. Press down lightly on the top of the dough and then wrap and freeze for 15 minutes, or until firm.
When firm, remove from freezer and unwrap, placing the dough on a cutting board. Using a sharp long knife, cut the layers lengthwise into 1/2 inch wide and 10 inch long strips. (You will end up with 4 strips).
Stack the layers, turning every other strip so top faces down and bottom faces up, to produce the checkerboard effect. Rewrap stack and place in freezer again to firm up.
Meanwhile, take the reserved chocolate trimmings and 1/2 cup of chocolate dough and roll out on a piece of parchment paper into approximately 9 1/2 x 10 1/2 inch rectangle, making sure the dough is smooth. Cover and refrigerate until slightly firm.
Remove stack of checkerboard dough from freezer and place in center of chocolate dough.
Wrap the chocolate dough around the checkerboard layers until you have a smooth surface that encloses the checkerboard design.
Wrap in plastic and freeze until firm.
Preheat oven to 350 degrees F
Line a baking sheet with parchment paper.
Remove dough from freezer and place on a cutting board.
With a sharp knife cut the block of dough into 1/4 inch thick slices.
Place on prepared baking sheet spacing about 1 inch apart.
Bake for about 5-7 minutes or until cookies just start to brown around the edges.