Method:

Preheat oven to 170 C.

For Vanilla dough, sift flour, and baking powder together. Make a well in the center and add icing sugar. Add water, egg yolk, vanilla and soft butter cubes. Mix all together, working your way from the inside of the well towards the outside, making a smooth dough. Once the dough comes together, do not overwork the dough. Cover with cling film and let rest in refrigerator for 2 hours or overnight.

For chocolate dough, sift flour, cocoa and baking powder and proceed as for vanilla dough.

After dough is well chilled and firm, knead dough to make it pliable and rollable.

For spirals:

Roll out vanilla dough to a thin layer. Do same with chocolate dough. Using egg wash, add one dough on top of the other and start rolling from one end to form spiral roll. Chill again for an hour. Cut into thin strips again and place on baking sheets.

For Checkerboards:

Roll out vanilla dough to thick rectangle. Cut into long strips. Do the same with the chocolate dough. Stack alternate doughs on top of each other, also using egg wash as an adhesive.

Roll out scraps of remaining dough to a thin layer, enough be be sufficient to cover the finished layers. Also chill and then cut into small slices and place on baking sheets.

Bake at 170 C. till light golden brown on the edges of the cookies.