In a large bowl, beat together the butter, golden syrup and sugar until fluffy.
Beat in the egg until well combined.
Add the flour, cocoa and the baking powder and mix well with a fork.
Add 130g (4.6oz) of the Smarties - reserve the rest for now. Fold them through.
You should now have a sticky, light dough that’s just firm enough to roll pieces in your hands. If not, cover the bowl and place it in the fridge for 15 minutes.
Form 2.5cm (1 inch) balls of cookie dough and place at least 5 cm (2 inches) apart on a baking paper lined baking sheet. I got 20 cookies in total, weighing about 40g (1.4 oz) each.
Flatten slightly with the palm of your hand.
Gently press three Smarties onto the top of each cookie.
Bake for about 12 minutes – too long and they’ll go hard and the chocolate may burn.
Allow to cool slightly for a few minutes (they firm up a little) and then put on a wire rack to cool.