Position rack in center of oven. Preheat the oven to 350°F (180°C). Lightly grease two non stick donut pans.
In a medium mixing bowl, whisk together the cocoa, flour, sugar, baking powder, baking soda, and salt. Set aside. ⅓ cup (23 g) dark cocoa powder (Dutch processed, not natural/unsweetened) ¾ cups (90 g) All-Purpose Flour ½ cup (100 g) granulated sugar ¼ teaspoon baking powder ¼ teaspoon baking soda 1/4 teaspoon fine sea salt
In a large mixing bowl, whisk together the eggs, buttermilk, vanilla and melted butter. 1 large eggs ¼ cup (60 ml) buttermilk ½ teaspoon Vanilla Extract ¼ cup (60 ml) unsalted butter
Add the dry ingredients to the wet ingredients, stirring with a spatula or wooden spoon just until the last of the flour is combined. Fold in chocolate chips if using. ¼ cup mini chocolate chips
Spoon the batter into the prepared pan(s), filling the wells about half full. Do not overfill. Or use a piping bag and pipe the batter easily into the donut pans.
Bake the doughnuts for 10-12 minutes, or until a toothpick inserted into the center of one comes out clean or with a few moist crumbs. Tops should Spring back when touched.
Remove the doughnuts from the oven and let rest in the pan for 1 minute then loosened edges (do not let rest too long or they will stick). Turn the pan upside down over a rack, and give the pan a gentle tap and shake to release the donuts. If one or two donuts stick, use the spatula or knife to loosen them further.
To make the icing: Heat heavy cream and chocolate chips in a microwave safe bowl for 1 minute. Let sit for 2 minutes. Do not stir during this time. Then whisk smooth. Add corn syrup and vanilla. Whisk until combined. 1/4 cup (60 ml) heavy cream 1/2 cup (85 g) semi-sweet chocolate chips 2 teaspoons corn syrup 1/2 teaspoon vanilla extract
Dip the top of each doughnut in the icing, spreading to coat; or simply spread icing on the doughnuts. Garnish with sprinkles if desired.