Preheat the oven to 350°F. Lightly spray 2 (6-well) donut trays with baking spray with flour.
In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.
In a medium mixing bowl, whisk together milk, egg, butter, and vanilla extract until well combined. Add the milk mixture to the flour mixture, whisking fully to combine. Transfer the mixture to a piping bag. Snip off the tip.
Pipe about ¼ cup of donut batter into each well. (The batter should fill each well to the top edge of the center pop out.)
Bake for 8 to 10 minutes or until donuts are puffed and a wooden pick inserted into the center of the donut comes out clean. Let cool for 5 minutes, then invert onto a wire cooling rack.
For the Chocolate Glaze:
In a small saucepan, bring 2 inches of water to a boil over high heat. Reduce heat to medium-low and continue to simmer.
In a medium heat-proof bowl, combine the chocolate chips, cream, and butter. Place on top of the saucepan, making sure it doesn’t touch the water. Stir the mixture until the chocolate and butter are melted and the mixture is smooth and combined. Remove the bowl from the saucepan.
Dip a cooled donut in chocolate glaze and place it back on the wire rack. Immediately top with sprinkles, if desired. Continue dipping and sprinkling. Let the donuts stand until the glaze is set, about 20 minutes. Store any leftovers in an airtight container for up to 3 days.
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Notes
If the donuts puff up and fill the hole during baking, you can trim with a small pairing knife or push the base of a piping tip through each donut to cut out the center after cooling.
Be sure to measure the flour correctly, or once baked, you might end up with dense donuts. Measuring flour with a scale is ideal as it is the most accurate method. If you don’t have a scale, fluff your flour with a spoon, sprinkle it into your measuring cup, and use a knife to level it off.
Be careful not to overmix the batter, as overmixing can cause the donuts to become tough.
Bring the milk and eggs out to room temperature before combining. This prevents you from overmixing the batter and promotes even baking.
Be very careful not to get any moisture into the bowl of chocolate chips, cream, and butter. If water gets in, the chocolate will seize, and you’ll have to restart making the chocolate glaze.
Make sure the donuts are as cool as possible before dipping them in the chocolate glaze. The glaze will melt off if the donuts are still hot instead of setting up nicely.
For even more chocolatey flavor to the donuts, you can add mini chocolate chips to the donut batter.