Sift the flour and add it to the mixture from step one in three batches, pressing the flour in each time (it will be a bit harder by the third addition).

Once mixed evenly, divide the dough into two portions. Add cocoa powder to one portion and mix well (as shown on the left in the picture).

Divide the dough into four parts and roll each into a long strip, then stack them together.

Place the dough in a plastic bag and shape it into a square. Freeze for 30-45 minutes until firm, then slice into pieces about 1/3 inch thick (I left it overnight; remember to let it thaw a bit before slicing for easier cutting).