To make the Donuts: Preheat oven to 350oF(180oC). Make your DIY Donut tin and grease it with butter. Watchman video to see how you can create your own Donut tin with a cupcake tin and tinfoil.
Sift together the flour, cocoa powder, baking soda, baking powder, both sugars and salt.
In a separate jug mix together egg, sour cream, melted butter, and vanilla extract.
Add the wet ingredients into the dry and gently mix to a smooth batter.
Add batter to a piping bag or ziploc bag. Cut a corner off to pipe into donut pan wells. Fill them no higher than 2/3 of the way up so they don't bake over.
Bake donuts for 10-12 minutes or until they are firm and spring back when you touch them. Pop them out of the donut pan and onto a cooling rack to cool until warm to the touch.
To make the Glaze: Sift together the icing sugar and cocoa powder. Whisk in the milk, vanilla and whisk until the glaze is smooth. You may need to add additional powdered sugar or milk depending on the consistency you like. Dip the top of each donut in the glaze. Serve it warm or at room temperature. Store in an airtight container for up to 3 days.