Preheat your oven to 350°F (175°C). Lightly grease and flour a 12-cavity donut pan, or two 6-cavity donut pans. If using only one pan, you will bake in two batches.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, cocoa powder, baking powder, and salt until well combined.

In a separate medium mixing bowl, whisk together the milk, large egg, melted butter, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and mix with a rubber spatula until just combined. Be careful not to overmix; a few small lumps are okay.

Spoon the batter into a piping bag (or a large Ziploc bag with a corner snipped off) or carefully spoon it into the prepared donut cavities, filling each about two-thirds full.

Bake for 10-12 minutes, or until the donuts are puffed up and spring back when lightly touched. If baking in batches, repeat with remaining batter.

Let the donuts cool in the pan for 5 minutes before carefully transferring them to a wire rack to cool completely.

While the donuts cool, prepare the glaze. In a small saucepan over low heat or in a microwave-safe bowl, whisk together the powdered sugar, cocoa powder, 3 tablespoons of milk, vanilla extract, and a pinch of salt. If using, add the melted butter.

Whisk until the glaze is smooth and free of lumps, adding more milk a teaspoon at a time if needed to reach your desired consistency. It should be thick enough to coat a spoon but still pourable.

Once the donuts are completely cool, dip the top of each donut into the chocolate glaze, allowing any excess to drip off. You can also drizzle the glaze over the donuts.

Place the glazed donuts back on the wire rack and allow the glaze to set for about 10-15 minutes before serving. For an extra touch, add sprinkles before the glaze sets!