In a large bowl/stand mixer, add your butter and sugar and cream together until they are creamy an smooth.
Add in the egg, and beat again. It might look a little funny here, but it will be fine don't worry.
In a different bowl, add your plain flour, baking powder, cocoa powder and salt, and whisk together until distributed evenly.
In a cup/bowl, add your milk and vanilla and whisk together as well.
Add half of the flour mixture, and half of the milk mixture to the butter mixture, and beat till smooth. Add in the other halves and beat again till smooth.
It should be a thickish chocolate looking cake batter when done.
With a large disposable piping bag, add the cake mixture. Grease your Mini Doughnut Moulds with cake release/low calorie oil spray/something.
Pipe in the mixture into the moulds. You want the mixture to be level with, or very slightly below the 'middle of the doughnut' so the it doesn't bake and overflow to form a weird blob.
Bake the doughnuts in the oven for 10-13 minutes. They should be a solid colour, and starting to come away from the edges of the moulds.
Once baked, remove from the oven and turn the moulds upside down onto a cooling rack. After about two minutes, carefully remove the doughnuts from the moulds.
Sometimes you might need to tap the top of the mould so that they doughnuts come out more easily. Once out, let them cool completely.
Carefully melt your chocolate of choice, and then dip the tops of the doughnuts in, and place chocolate side up onto a tray. Sprinkle with you chosen sprinkles and leave to set.
Some Doughnut Moulds are different shapes and sizes – so keep an eye on the Doughnuts after 10 minutes. Also, how much people will put in each mould also varies – practice with time and you will perfect the amount to use in each one! I bought my Mini Doughnut Moulds on Amazon!
These will last for 2-3 days at room temperature, but are best on the day of baking!