Preheat the oven to 180º / Gas 4 and line 2 baking trays with baking paper.
Mix the flour, baking powder and bicarbonate of soda in a bowl.
In a separate bowl, using an electric whisk beat together the butter and both sugars until light and fluffy.
Gradually add the egg until all combined.
Fold in the flour mixture until all mixed together to form a biscuit dough.
Take a tablespoon of the mixture and roll into a ball. Arrange on the trays, spaced well apart as they will spread.
Flatten each ball with a back of a fork and top each with a couple of smarties.
Place in the oven and bake for 10-12 mins until golden. Leave to cool and store in an airtight container.