Preheat the oven to 350ºF (177ºC).
Prepare three 8″x2″ cake pans with cake goop or another preferred pan spray.
Melt your chocolate in a heatproof bowl in 15-second increments until just melted. Do not overheat or you could burn your chocolate.
Then, add your warm water to the chocolate and whisk to combine. Set aside.
Next, place the room temperature egg whites in a separate bowl with the whisk attachment and whip until you reach firm but moist peaks. They shouldn’t look broken or crumbly. Set aside. Combine the room temperature buttermilk and the vegetable oil and then set aside.
Whisk together the flour, baking soda, and salt and then set aside.
Then, in the bowl of your stand mixer, cream together the room temperature butter and sugar until it is light and fluffy in color.
Add in your egg yolks one at a time, letting each mix in fully before adding in the next.
While mixing on low, add in your melted and cooled chocolate and vanilla and then mix until it’s combined.
Next, while mixing on low, add in 1/3 of the flour mixture, and then 1/3 of the buttermilk mixture. Repeat two more times with the remaining flour and buttermilk.
Gently fold in your egg whites until they are blended.
Pour the batter into your prepared pans.
Bake the cakes immediately at 350ºF (177ºC) for 30 minutes, or until a toothpick comes out from the center clean.
Let the cakes cool for 10 minutes inside of the pan before flipping them out.
Flip the cake onto a cooling rack and let it cool completely. I chill my cakes before handling them, or you can wrap them in plastic wrap and freeze them to trap moisture in the cake.
Thaw the cake on the countertop while it’s still wrapped before frosting.