Preheat the oven to 350ºF (175 °C). Brush 10 cavities of two donut pans with canola oil and set aside.
In a large bowl, whisk together the flour, baking soda, cocoa powder, salt, granulated and brown sugar. Set aside.
Melt together the butter and the dark chocolate. Set aside to cool slightly.
In a bowl, whisk together the sour cream with the egg and vanilla extract. Add this mixture to the bowl with the dry ingredients, as well as the melted chocolate mixture. Mix together with a wooden spoon.
Transfer the donut batter to a piping bag and pipe the mixture into the greased cavities of the donut pans.
Bake the donuts for 10 minutes or until a cake tester inserted comes out clean. Let cool slightly before unmolding then cool completely on a wire rack.
Dark chocolate glaze
Melt the dark chocolate in a bowl over a double boiler. Remove the pan from the heat when the chocolate is melted and take the bowl down off the pan.
Stir the butter into the chocolate until it has melted, then add the milk. Mix well. Dip the donuts into the glaze. Top with chocolate sprinkles.
Notes
To bake donuts, you will need to buy a donut pan. I used two Nordicware donut pans that you can buy on Amazon
For the recipe, I used Cacao Barry Ocoa chocolate, which is a professional quality chocolate that you can find at IGA grocery stores in Quebec, or online at Vanilla Food Company. And the price per gram is actually much more reasonable than baking chocolates. Plus the flavour is much better!
For cocoa powder, I use either Cacao Barry Plein Arôme (Amazon) or Cacao Barry Extra Brute (Amazon).