Preheat the oven to 170°C / 150°C fan.
Prep a cupcake tray with cupcake cases.
In a medium bowl, sieve and whisk together flour, cocoa, xanthan gum, baking powder and salt.
In the bowl of an electric mixer, beat butter and sugar until pale and fluffy (about 4 minutes).
Beat the eggs in a small bowl/jug and pour about a third into the butter and sugar mixture. Follow with a heaped tablespoon of the flour mixture (this will stop it from curdling). Beat until well combined. Repeat this process twice more until all of the egg has been added.
Add the Greek yoghurt. Mix to combine.
Add the rest of the flour mixture and mix gently until just combined.
Distribute the batter evenly into the cupcake cases. The recipe makes approx. 9-10 cakes. Each case should be about 3/4 of the way full.
Bake for approx 20 minutes or until a skewer comes out clean.
Leave to cool for at least an hour before filling and decorating.