Whisk together the egg, greek yoghurt, vanilla extract and melted butter
Add self raising flour and caster sugar and mix to combine until you form a smooth dough
Using oiled hands, roll the dough into 10 ball shaped doughnuts (weigh the total volume of dough, divide by 10 and then weigh out individual balls)
Preheat vegetable oil to 170-180C and deep-fry the doughnuts for approx. 4 minutes until golden (do this in 2 batches)
Remove from oil and coat in caster sugar straight away
Melt chocolate with double cream over a low heat and serve alongside the greek yoghurt doughnuts
