Combine the Main Ingredients: In a large bowl, or the bowl of a stand mixer fitted with the paddle attachment, combine the dry cake mix, the thawed Cool Whip, and the egg.

Mix the Dough: Mix on a low speed until everything is just combined. The dough will be very soft and sticky, almost like a thick brownie batter. Avoid over-mixing; stop as soon as there are no dry streaks of cake mix left.

Chill the Dough: This is the most important step! Cover the bowl with cling film and place it in the refrigerator to chill for at least 30 minutes. This will firm up the dough, making it possible to roll into balls.

Preheat and Prepare: Towards the end of the chilling time, preheat your oven to 180°C (160°C fan). Line two large baking trays with parchment paper.

Coat the Cookies: Place the icing sugar in a shallow bowl. Take about a tablespoon of the chilled dough and roll it into a 1-inch ball. What works best for me is using a small cookie scoop to portion the dough evenly. Drop the ball into the icing sugar and roll it around until it's generously and completely coated.

Arrange on Trays: Place the sugar-coated dough balls onto the prepared baking trays, leaving about 2 inches of space between each one to allow for spreading.

Bake the Cookies: Bake for 10-12 minutes. The cookies will puff up and the tops will crackle, revealing the dark chocolate cookie beneath the white sugar. They should look set around the edges but still be soft in the centre.

Cool Properly: Let the cookies cool on the baking tray for 5 minutes. They will be very soft when they first come out of the oven, and this allows them to set. Afterwards, carefully transfer them to a wire rack to cool completely.