Chocolate chip shortbread

1. Preheat the oven to 190 ºC. In an electric mixer, beat the butter well until very soft.
2. Add the sugar a little at a time, beating well, until all of it has been added.
3. Beat well until mixture is light and fluffy, about 3 minutes.
4. Sift the flour together 3 times, then add to the sugar mixture. Finally, add the chocolate morsels.
5. Mix on slow speed until the flour is mixed in and a stiff dough is formed. Do not overmix.
6. Grease an 18 x 22 cm swiss roll pan and press the mixture in with the back of a tablespoon. Prick dough all over with a fork and mark out slices with a sharp knife, but don’t cut through.
7. Sprinkle top with a little castor sugar and bake at 190 ºC for 10 minutes. Then reduce temperature to 160 ºC and bake for another 15 minutes until golden in colour.
8. Cut into marked slices when cooled.