First, preheat the oven to 180°C (350°F) and lightly grease a donut pan.
Next, in a large bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt until well combined.
In another bowl, mix the eggs, milk, oil, and vanilla extract until smooth.
Then, pour the wet ingredients into the dry ingredients and gently mix until just combined. Do not overmix.
After that, transfer the batter into a piping bag or spoon it carefully into the donut pan, filling each cavity about ¾ full.
Bake for 10–12 minutes, or until a toothpick inserted comes out clean.
Finally, remove from the oven and let the donuts cool for 10 minutes before glazing or serving.