In a large bowl, beat together the butter, golden syrup and sugar until fluffy.
Beat in the egg and the Baileys until well combined.
Add the flour, cocoa and the baking powder and mix well – you should now have a sticky, light dough.
Fold in the dark chocolate chunks, keeping a handful (about 50g) back to go on top later.
Use a large ice cream (this is the best way to get equally sized cookies) scoop the dough, flattening off against the side of the bowl, and drop onto a baking sheets lined with greaseproof paper, being sure to place each cookie at least an inch apart so that they don’t stick together when they spread.
Press the cookies down with the heel of your hand so that they're 2 cm (3/4 inch) thick.
Bake for 12-14 minutes until golden at the edges. Get them out of the oven before they’re fully browned so that they stay chewy when cool.
While still hot, place a tumbler over a cookie and gently move it in small circles to bring the cookie into a neat circle. Repeat with all of the cookies - this only works when they are fresh from the oven and soft.
Top with the remaining dark chocolate chunks.
Allow to cool on the tray until firm enough to transfer to a wire rack to cool completely.