Preheat your oven to 350 degrees.
Grease and line your baking pans with parchment paper (two or three 8” or 9” baking pans, depending on how thick you want the layers of your cake).
Separate 4 eggs into yolks and whites.
Place 4 ounces of roughly chopped chocolate into a small bowl and pour 1/3 cup of hot coffee or water over the chocolate. Let it sit for a minute and then whisk until completely smooth. Set aside for now.
In a large bowl, whisk 1 cup of softened butter with 1 cup of granulated sugar, 1 cup of brown sugar, 4 egg yolks and 2 teaspoons of vanilla extract until creamy
Add 1 cup of buttermilk and the melted chocolate mixture and whisk until completely combined
Sift 2 1/2 cups of cake flour, 1 teaspoon baking soda and 1/2 teaspoon salt into the bowl and mix until just combined
In a separate, very clean bowl, whisk 4 egg whites until you have stiff peaks and then carefully fold the stiff egg whites into the batter
Divide the batter evenly between your prepared baking pans.
Bake in a 350 degree oven for 25-35 minutes, depending on the size of your baking pans. The cakes are ready to come out when a toothpick will come out of the center of the cake clean.
Transfer the cakes onto a cooling rack to cool completely before frosting (leave the oven turned on for the frosting)