Preheat the oven to 350°F and grease two nine-inch cake pans. Line the bottom of each one with parchment paper.
Divide the egg yolks from the whites of each egg. Place the egg whites in a mixing bowl and set the yolks aside in a separate small bowl. Beat the egg whites with an electric hand mixer until they form a peak. Set aside.
In a large bowl, combine three-quarters of a cup of softened butter and one and one-half cups of granulated sugar. Mix until creamy and smooth. Add the egg yolks and two teaspoons of vanilla extract. Beat for two minutes.
In another mixing bowl, sift together two and one-half cups of Bisquick and one teaspoon of baking soda. Add half of the dry mix to the creamed butter. Mix until incorporated. Add half of the buttermilk; continue mixing and repeat until the remaining dry ingredients and buttermilk are well combined without overmixing.
Gently fold in the egg whites with a spatula.
Divide the batter evenly between the pans.
Bake for thirty minutes or until the middle of the cake has set.
Allow the cakes to cool before turning them out onto a wire rack.
To prepare the frosting while the cakes cool. In a large bowl, using an electric mixer, beat one cup of softened butter and two teaspoons of vanilla extract together until creamy and smooth.
In a separate bowl, sift together four cups of confectioners’ sugar and three-quarters of a cup of cocoa powder.
Alternately add the dry ingredients to the creamed butter with the electric mixer. Add the milk if needed to acquire the desired consistency.
Once the cakes have completely cooled, frost and assemble as you would like.