Preheat your oven to 180°C. Line a baking sheet with baking paper.
In a large bowl beat together the softened butter, sugar and zest with a wooden spoon until it come together like a paste. Add the egg and beat together.
Add the flour, baking powder and chocolate and stir together, be careful not to overwork the mixture.
Divide the dough into 12 - 20 roughly shaped blobs and place on your backing tray with plenty of space between each one.
Cook for about 15 minutes or until the edges are turning light brown.
Leave to cool and then enjoy.