• In a bowl mix together the flour, baking powder, baking soda, and salt and set aside.
• In a separate bowl, whisk together the milk, discard starter, sugar, egg, butter, and vanilla, and milk until well combined.
• Add the dry ingredients into the wet ingredients and fold until it's combined, but don't overmix.
• You can now bake the donuts straight away, or ferment the batter first.
• Fermenting the batter
• The batter can be fermented in the fridge for 4 hours or overnight before baking. This gives the bacteria in the starter time to start breaking down the starches in the flour and can help with digestibility. Cover the bowl and place it in the fridge.

Baking the donuts

• Heat the oven to 356°F/180°C and grease a 6 donut tin.
• Scoop the batter into the tin with a small spoon or fill a piping bag with a large nozzle and pipe the batter into the cavities.
• Bake the donuts for around 10 minutes until puffed and just lightly golden around the edges.
• Let them cool in the tray for 5 minutes before removing so they don't break. Use a silicone or rubber spatula to run along the edges of the donuts to make removal easier.
• Let them cool upside down (with the domed side facing up) on a wire rack and make the glaze.

The glaze

• Mix together powdered sugar, cocoa powder, vanilla, and enough milk to make a pourable glaze.
• Dip the domed side into the glaze, then let them dry on a wire rack.