Preheat the oven to 180C/350F and spray your doughnut pans with cooking spray - I have 2 Wilton 6 hole doughnut pans, so had to bake 12 doughnuts, then bake another 6 when they were baked.
Place the cake mix, egg, oil and milk into a large bowl and add in any extracts you are using.
Mix with a spatula/wooden spoon until the mixture comes together and there are no lumps of flour. The mixture will be thick and sticky.
Place the mixture into a large piping bag and snip the end off so the hole is around 1/2 inch across. Gently squeeze the dough into each doughnuts hole, don't fill the pans level, you want to fill them about 3/4 of the way up.
Place in the oven for 10-12 minutes (mine took 11) until risen and an inserted skewer into the centre comes out clean.
Place kitchen paper underneath your wire rack, leave the doughnuts to cool for 5 minutes in the pan and then tip onto your wire rack to cool completely so the rounded side that was in the pan is now your top.
To make the white glaze: whisk the melted butter, icing sugar and 1tbsp of milk together until smooth in a small, flat bowl. Add extra milk as required until you have a glaze which will ribbon as you pull the spoon out. You want it to stick to the top of the doughnut and not drip off completely. A little drip is fine. Take each doughnut and dip gently into the glaze, pull out and flip, then return to your wire rack. Repeat until all of your doughnuts are glazed.
To make the chocolate glaze: whisk melted butter, icing sugar, cocoa powder and 1tbsp of milk until smooth, add milk 1tbsp at a time until you have a thick glaze which ribbons as you pull the spoon up out of the bowl.
Tip your chosen sprinkles into a flat bowl and then dip the top of your glazed doughnuts into the bowl of sprinkles.
Leave to set for 15 minutes before digging in. Cake Mix Doughnuts will keep in an airtight container, in the fridge for 3 days.