It's all about the form! From rigid cardboard or plastic sheet (I went in the course of plastic kitchen Board) to do just such a form, as in the photo. The number and size of squares do as what shape you want to see your cookie =)

Heated to 180 degrees oven and in parallel prepare the dough for the cookies. The butter and powdered sugar, whisk to lighten and kind of "fluffy". Gradually add egg whites and vanilla. Next, slowly and gently add the sifted flour. Knead a smooth dough. 1 teaspoon of the dough mix with cocoa and leave it alone.

Place the stencil on parchment paper. To put the dough into the holes on the stencil and using a knife, flatten the dough into squares. Remove the stencil, paper with the dough to move it to the baking sheet. The dark dough with cocoa to draw zigzags on the squares of dough. Put in the oven for 8-10 minutes until Golden brown.