Preheat your oven to 180°C and line a baking tray with baking paper.
Cream the butter and castor sugar together until pale and fluffy.
Mix in the egg and vanilla extract. Add the flour and baking powder and mix to combine. Lastly, mix in the chocolate chips.
Wet your hands slightly and roll tablespoonfuls of dough into balls. Arrange on the tray allowing room for spreading. Flatten each ball slightly with a fork that has been dipped in flour.
Bake for 10 minutes. then rotate the tray 180 degrees and bake for a further 4 minutes or until the cookies are golden at the edges. Carefully transfer the cookies to a cooling rack. (They will be very soft but will harden on cooling.) Allow to cool before serving.