In a medium bowl, sift flour, cocoa and baking soda.
In a separate bowl, combing egg, brown sugar and granulated sugar. Beat with an electric mixer until light and fluffy. Add vanilla and melted butter. Beat until smooth.
Add dry ingredients to wet. Add buttermilk and beat until just combined.
Spray donut pan with nonstick cooking spray. Pipe batter into donut pan, filling each mold ¾.
Bake for 10-12 minutes, until donuts spring back to the touch. Place on cooling rack. Cool completely before making chocolate glaze.
For the glaze
In a heat safe bowl, combine chocolate chips, whipping cream and butter. Microwave on high, stirring every 15-20 seconds, until smooth.
Allow glaze to cool 3-5 minutes. Dip top half of each donut into glaze twize. Garnish with sprinkles.