Grease and flour several baking sheets.

In a large bowl mix the butter and sugar until light and fluffy. Gradually add the lightly beaten egg in 3 portions into the creamed mixture, beating well after each addition.

Sift the flour into the creamed mixture and mix thoroughly until a soft dough is formed. At this point use your clean hands to mix it together. Add extra flour if the dough is too sticky. But be careful not to make the dough too hard.

Divide the dough into two eaqual portions.

Put the plain chocolate in a heatproof bowl and melt it. The best way to melt chocolate, without burning it, is to set it over a saucepan of gently simmering water until melted. Otherwise we can simply put the heart proof bowl in a microwave. Heat it for 30 seconds, give it a nice stir and put it again for another 30 seconds, if not melted completely. Take care to stir it well to avoid burning it. Mix the chocolate and sifted cocoa powder into one half portion of the dough. Do not add all of the cocoa powder, add only till you get the chocolate brown colour. Knead it to make a soft dough. Since the chocolate is a bit liquid, you may have to add extra flour.

Into the other portion, add the grated lemon rind and mix well till you get a soft dough.

Now, on a lightly floured surface, roll out/ flatten the chocolate dough and the lemon rind dough into a rectangular shape SEPERATELY. You can also roll it on a baking paper to avoid the dough sticking on to the surface. Take care to roll/ flatten it as exactly as possible.

Place the flattened lemon rind dough over the chocolate dough and roll it tighty using the baking paper to guide you. Chill the rolled dough for a hour.

Preheat oven to 190ºC. Cut the rolled dough into pieces of nearly 1 inch thickness and place it on the baking paper. Bake in the pre-heated oven for10-12 minutes or until lightly golden in colour. Transfer to a wire rack and leave it to cool completely before serving.

It is important to take note that cookies & biscuits cook even after being taken out of the oven, during the cooling process. So even if you find the cookies are not cooked when immediately out from oven, don't worry, just wait for it to cool. Also don't over cook, then it will be hard and brittle. If you are using a fan forced oven, bake at 170ºC.