Add the softened butter and caster sugar to a large bowl and cream together until smooth and fluffy. If you don't have a mixer, you can rub the butter and sugar together with your fingers until combined.
Add the plain flour, and cornflour, beat or mix until the dough comes together. It may be slightly crumbly at first, just knead gently with your hands to form a smooth dough.
Fold in the chocolate buttons (milk and white chocolate) until evenly distributed throughout the dough.
Lightly flour your work surface and roll the dough out to a thickness of 1.5cm.
Use a 7cm cookie cutter to cut out the cookies and place them on lined baking trays. Space them out, about 6 per tray, as they are quite large.
Place the cut cookies in the fridge for 30 minutes. While chilling, preheat your oven to 180°C (160°C fan/ Gas Mark 4).
Sprinkle a little extra sugar over the tops of the cookies. Bake for 20–25 minutes or until golden.
Leave the cookies to cool on the trays for a few minutes before transferring to a wire rack. Once cooled, enjoy your shortbread cookies with a cup of tea or coffee!
