Preheat the oven to 350 F (177 C). Grease a 6 ct. donut pan.
In a large bowl, whisk the flour, cocoa powder, baking powder, baking soda and salt.
In another large bowl, pour the melted butter, granulated sugar, egg, yogurt, milk and vanilla extract. Whisk well to fully combine.
Add the dry ingredients to the wet. Whisk well until smooth and just combined.
Pipe the chocolate donut batter into each of the prepared donut cavities in the donut pan. The easiest way it to use a piping bag or gallon zip lock bag with the tip cut off.
Bake the donuts for about 8-10 minutes. The donuts are done when the tops bounce back quickly when lightly pressed. Cool the donuts in the pan for 5 minutes before gently taking them out to cool on a cooling rack. While the doughnuts cool, make the chocolate glaze.
In a microwave safe bowl, add the chocolate chips, heavy cream and evenly cubed butter. Heat the mixture for 30 seconds. Stir until mostly combined. Return the bowl to the microwave, heat for another 15-20 seconds. Stir until well combined and glossy. Don’t worry if the mixture seems a little grainy or curdled, just keep stirring in the same direction until the glaze becomes smooth.
Dip each fully cooled chocolate cake donut into the chocolate glaze. Top with sprinkles or mini chocolate chips now if you like. Allow the chocolate donuts with chocolate glaze to set for about 30 minutes.