the eggs one at a time followed by vanilla extract.
add the flour to the butter mix and mix until just combined. split the mixture into two and add the cocoa powder to one half.
wrap both doughs in cling film and chill for at least an hour.
on 2 sheets of non-stick baking parchment draw a 7 x 5 inch rectangle and flip the paper over so the ink is facing down. unwrap the dough and place in the middle of each rectangle. place another sheet of baking paper on top of the dough and roll out the dough to fit within the marked rectangle. use the edge of a knife to 