1. Preheat your oven to 350°F (175°C) and grease a donut pan.
2. In a large bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.
3. In another bowl, mix the milk, melted butter (or oil), egg, and vanilla extract.
4. Pour the wet ingredients into the dry ingredients and mix until just combined. Fold in the chocolate chips, if using.
5. Fill the donut cavities about 3/4 full. Bake for 12-15 minutes or until a toothpick inserted comes out clean.
6. Let the donuts cool in the pan for a few minutes before transferring them to a wire rack to cool completely.
7. For the glaze, whisk together the powdered sugar, cocoa powder, and milk (or water) until smooth. Adjust the consistency with more milk or powdered sugar if necessary.
8. Dip each donut into the glaze and return to the wire rack. If desired, top with sprinkles. Allow the glaze to set before serving.

Notes

• Feel free to customize this recipe with different glazes or toppings. White chocolate, caramel, or even a simple sugar dusting could make delightful variations.
• These donuts are best enjoyed fresh but can be stored in an airtight container for up to 2 days.