Sieve gluten-free flour, cocoa powder, xanthan gum, baking soda and salt into a mixing bowl. Whisk together ensuring ingredients are well mixed. Set this aside for later.
Place the melted butter, cream cheese, brown sugar, caster sugar and vanilla extract in the bowl of an electric mixer. Mix at a medium speed for 3 minutes.
Add the egg and mix at a low speed until incorporated. Repeat with the egg yolk.
Add the flour mixture you prepared earlier to the mixer bowl. Mix on a low speed until just combined, stopping to scrape down the sides if necessary.
Finally, briefly mix through the Aero chunks and chocolate chips on a low speed until evenly incorporated.
Cover the bowl and chill in the fridge for at least 4 hours.
Once ready to bake, preheat the oven to 170°C. Roll the dough into evenly sized balls (each cookie should be approx 60-65g) and place on a lined baking tray. Make sure to leave enough room for spreading between each dough ball.
Bake for 11-12 minutes, keeping a close eye on them. Remember that if the cookies seem a little too gooey they will firm up more as they cool.
If adding extra Aero Mint chocolate on top, carefully push the chunks onto each cookie when they are fresh out of the oven.
Leave to cool on the tray for approx 15 mins before transferring to a cooling rack for another 30 mins to an hour.