cake adapted from BakeWise
546g (2 3/4 cups) granulated sugar
4.5g (3/4 teaspoon) salt
69g (3/4 cup) dutch processed cocoa powder
5g (1 teaspoon) baking soda
237ml (1 cup) boiling water
237ml (1 cup) canola oil
10ml (2 teaspoons) vanilla extract
2g (2 teaspoons) instant expresso powder or crystals
218 grams (1 3/4 cups, spooned and leveled) bleached all purpose flour
4 large egg yolks
2 large eggs
1/4 cup buttermilk
non-stick spray
Preheat your oven to 350°F. Place a rack in the lower third of the oven and set a baking stone on it. (The stone helps the cake bake evenly and prevents humped tops. If you don’t have a stone, the cake will survive don’t worry. Just be prepared to trim any uneven tops and make sure the cake gets an adequate amount of time in the oven to fully cook.)
You’ll need two 9″ or two 8″cake pans for this cake. Spray the pans with non-stick spray oil and then line them with parchment (sides and bottom–this is a sticky cake) then spray the parchment with even more non-stick spray.
In a medium sauce pan, combine the sugar, dutch processed cocoa, salt and baking soda. Stir with a whisk until combined and then slowly add the boiling water while whisking. This will bubble up a bit while the baking soda reacts with any remaining acidity in the dutch processed cocoa. Once throughly mixed, place the sauce pan over medium-high heat and bring back to a boil. Then remove from heat and allow to stand for a minimum of 10 minutes. This step makes the dutch processed cocoa even more alkaline, so our cake will be nearly black.
While waiting on the chocolate mixture, get your mise en place goin’ on! Measure out the flour,  buttermilk (no weird substitutions, folks. We need the acidity), and separate the eggs. (If you’re odd like me, you’ll remove the stringy white chalaza from the yolks. Sometimes they show up as white scrambled egg bits maring my otherwise perfect black cake.)  Add the oil and vanilla to the bowl of your stand mixer with the paddle attachment (this can also be done by hand with a wooden spoon).
When the chocolate mixture is ready, stir in the instant espresso powder. (This won’t make the cake taste like coffee, rather it enhances the chocolate flavor of the cake. Dutch processed cocoa has great color but it isn’t quite as flavorful as it’s light-colored acidic cousin, natural cocoa.) Add the chocolate mixture to your stand mixer and mix on low speed for about 20 seconds. Add the flour and continue to mix on low until combined. With a minimum amount of beating, add the egg yolks, eggs, vanilla and butter milk. The batter will be very thin.
Divide the batter between your two pans and place in the oven on your baking stone.  Bake for 25-30 minutes (for 9″ rounds. Add 5-7 more minutes for 8″ rounds) until the center of the cake springs back when you touch it.  Allow the cake to cool for 10 minutes on a wire rack. Run a thin knife around the edge of the cake to loosen and invert onto a flat dish lined with parchment.
Allow to cool completely then wrap the rounds individually in plastic and place in the refrigerator to chill before assembling.

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