1.Preheat oven to 180°C. Grease oven trays; line with baking paper.
2.Beat butter, extract, sugars and egg in a small bowl with an electric mixer until light and fluffy. Transfer mixture to a large bowl; stir in sifted flour and soda, in two batches. Stir in chocolate.
3.Roll tablespoons of mixture into balls; place 5cm apart on trays.
4.Bake cookies 15 minutes or until golden; cool on trays.
For a chewier cookie, bake for 12 minutes. Cookies will keep in an airtight container for up to 1 week.