Line two baking trays with greaseproof paper/baking parchment and set aside.
In a large mixing bowl, cream together the butter and sugars until light and fluffy.
Add the egg and beat in.
Sieve in the flour and cocoa powder, then spoon in the baking powder, bicarbonate of soda, salt and the cornflour (if using) and mix in until a dough is achieved.
Press in the chocolate chunks/chips/candy.
Shape your dough into 10 equal balls. Sit them on the trays with 6 on each tray, leaving a generous amount of space in between each ball.
Chill the cookie dough pieces in the fridge for at least 1 hour or in the freezer for 30 minutes. Do not skip this step as you could end up with super flat cookies!
While your cookies are chilling, shape 10 pairs of ears using your green fondant or modelling chocolate. To help with this, I used a chopstick to create the indent in the top of each ear (you could use the rounded end of a cutlery utensil or paintbrush). Set aside uncovered.
After about 50 minutes of chilling, preheat the oven to 200°C [390°F] or 180°C fan.
When ready, bake the cookies for around 8 to 10 minutes, until slightly dry looking on the top. They shouldn’t need pressing down before baking, but this is down to personal preference. Avoid baking for longer than the allotted time: they will continue baking on the trays after.
After the allotted time, take your cookies from the oven. Sit a pair of ears into the centre of each one while they are still warm, leaving a small gap between each ear. Allow the cookies to cool with the ears in them for at least 30 minutes before enjoying!