Preheat the oven to 350°F (175°C). Lightly grease a donut pan with nonstick spray or melted butter.

In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking powder, and salt until evenly combined.

In another bowl, whisk together the milk, eggs, melted butter, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and stir gently until just combined. Be careful not to overmix; the batter should still have a few small lumps.

Spoon the batter into the prepared donut pan, filling each cavity about ¾ full. Alternatively, use a piping bag or plastic zip-top bag with the corner snipped off to pipe the batter into the cavities.

Bake for 12-15 minutes, or until the donuts are set and a toothpick inserted into the center comes out clean.

Allow the donuts to cool in the pan for 5-10 minutes, then transfer them to a wire rack to cool completely.

To make the glaze, whisk together the powdered sugar, cocoa powder, milk, and melted butter in a medium bowl until smooth. Adjust the milk as needed to achieve your desired consistency.

Dip the tops of the cooled donuts into the glaze, letting any excess drip off. Place the glazed donuts back on the wire rack to allow the glaze to set.

Serve immediately or store in an airtight container at room temperature for up to 2 days. Enjoy!