Preheat your oven to 180 C / Gas 4. Grease or line a baking tray with parchment.
Cream together the butter and sugars. Add the egg and vanilla extract, and mix together.
Add the flour, cocoa, baking powder and salt and mix well. The cookie dough will become a bit stiff but just mix until everything is combined, and finally add the Daim® bar pieces.
Place small balls on the baking tray and flatten each ball (these cookies will not spread out a lot in the oven).
Bake for about 10 minutes. Take them out, they will not look cooked but they will harden in a few minutes out of the oven.