Preheat oven to 350° F. Spray a 6-cavity donut pan with nonstick cooking spray.
In a large mixing bowl, add the gluten free flour blend, cocoa powder, baking powder, baking soda, and salt and whisk to combine.
In a medium mixing bowl, whisk together the egg and sugar until completely combined and the color has lightened (about 2-3 minutes).
Whisk the vanilla, milk, sour cream, and melted butter into the egg mixture.
Using a rubber spatula, fold the wet ingredients into the dry ingredients until just combined.
Transfer the batter to the prepared pan with a spoon, pastry bag, or large plastic storage bag. Snip the corner off the bottom of the storage bag and pipe the batter into the donut cavities.
Bake for 10-12 minutes, or until the donut springs back when touched.
Allow the donuts to cool in the pan for 4 minutes before inverting onto a wire rack to cool completely.
Make the Glaze:
In a small mixing bowl, whisk together powdered sugar and cocoa powder.
Add milk and vanilla and whisk until smooth. Add a touch more milk if needed to achieve the desired consistency.
Dip one donut in the glaze then place back on the wire rack and top with sprinkles. Repeat with each remaining donut.
Notes
Grease the donut pan with nonstick cooking spray to prevent any part of the donut from sticking. Even though the donut pans I use are non-stick, I still take the time to lightly spray them with cooking spray.
Use a piping bag to transfer the batter to the donut pan. The bag makes filling the donut wells easy. If you don’t have a piping bag you can spoon the batter into the pan or use a large plastic storage bag with the corner snipped off.
Cool the donuts for a few minutes before inverting the pan onto a wire rack. The donuts are delicate when they come out of the oven and may break or crumble if removed from the pan too soon.
Dip one donut in the chocolate glaze and add the sprinkles. Repeat the process with the remaining donuts. If you dip all the donuts before adding the sprinkles the glaze may set and the sprinkles won’t stick.