Pre-heat your oven to 180C Fan/400F/Gas Mark 6, and line a few baking trays (or however many you own) with baking paper
Set aside 14 pieces of the chocolate oranges, then chop up the rest into chocolate chip sized chunks
Ideally using a stand mixer with the paddle attachment, mix the butter, caster sugar and light brown soft sugar together until fluffy and paler in colour. This will take 3-5 minutes in an electric mixer (I use speed 3)
Add the egg and orange extract, and mix them in
Add the plain flour, cocoa powder, baking powder, bicarbonate of soda and salt and mix them in until just combined
Add the chopped up Terry's Chocolate Orange pieces, mix briefly, just to evenly distribute them
Divide the dough into portions, I weighed the dough out to make each cookie an equal size. For 14 cookies I used 60g dough per cookies. If you'd like bigger cookies, you can make 12 cookies with 70g dough per cookie
Roll balls of the cookie dough between your hand, flatten them a little and place onto your lined baking trays, leave space between the cookies (at least 2") as they will spread
Bake the cookies for 12 minutes, remove from the oven and place a segment of Terry's chocolate orange on top of each one, then leave to cool on the trays for at least 10 minutes before moving to a cooling rack
Store leftovers in an airtight container and eat within 3 days