Preheat oven to 350 degrees and prepare a donut pan by spraying with nonstick cooking spray.
In a large bowl, whisk together gluten-free baking four, cocoa powder, baking soda, baking powder, brown sugar, sugar, cinnamon, and salt.
In a separate bowl, combine melted butter, eggs, milk, and sour cream.
Combine wet ingredients with dry ingredients and beat until smooth.
Pour batter into a piping bag and pipe into the donut pan, filling each space around 2/3 of the way full.
Bake donuts for 12 to 15 minutes or until the donut springs back when touched.
Allow the donuts to cool slightly in the pan, then remove them to a wire cooling rack to cool completely.
While the donuts are cooling, make the glaze by combining the powdered sugar, cocoa powder, and milk in a medium bowl.
Whisk the ingredients together until smooth then dip each donut in the glaze. Top with sprinkles if desired.