Add the butter and cream the butter in the mixing bowl. Keeping the pace on medium.
Add the sugar.
Add the 4 egg yolks one yolk at a time. Making sure to incorporate each yolk before add the next.
Add the coffee and chocolate. Then the vanilla extract.
Add the flour mixture slowly making sure to incorporate fully until. Add a little buttermilk at a time. Alternating between the buttermilk and flour until to fully incorporated. Keeping the mixer on low to medium.
Once completely mixed- set aside. If necessary place cake batter in a separate bowl if you only have one mixing bowl.
Clean the mixing utensils and mixing bowl.
Now using a clean mixing bowl add the 4 egg whites. Start the mixer on low then turn up to the high speed until the texture changes to “fluffy white” and stiff peaks form.
Grab the bowl of cake batter and add one large dollop of the egg whites. Mixing from bottom to top slowly and carefully incorporate the egg whites to the batter. Once thoroughly mixed add the rest of the egg whites and continue the process of stirring from bottom to top until fully incorporated. This is not an aggressive process- mix very slowly and carefully.
Then take your cake pans and evenly distribute the batter amongst them. Note: I use a kitchen scale to ensure that the batter is even but that’s not mandatory but super helpful.
You can then use the cake belts and place them around the cake pans. This is also optional but helpful to ensure your cake doesn’t “dome.” Place the cake pans in the preheated oven.
Allow the cake to bake for 22-25 min or until the toothpick test comes out clean.
Once done take the cake out of the pans after 10 min of cooling and remove them to wire wracks to totally cool.
Now start on the icing.