Line 2 large baking sheets with nonstick baking paper. Place the butter, sugar, orange rind and orange extract in a bowl and beat together with a hand-held electric whisk until light and fluffy. Add the egg and beat well, then sift in the flour, baking powder and salt. Add the chocolate chips and mix until combined.
Drop 20–22 small spoonfuls of the mixture, well spaced apart, on to the prepared baking sheets.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10 minutes, or until golden. Transfer to wire racks to cool.