Pre-heat the oven to 350°.
If you're making buttermilk, make it first and set aside.**
Cream (or mix) the butter and sugar together for a good 5 to 8 minutes.
You can also cream the oil, egg yolks, vanilla extract, and butter extract in with the sugar mixture if you want, or you can add them in after the butter and sugar mixture is already creamed.
Meanwhile, sift the dry ingredients together at least 3 times.
Then alternate adding the dry ingredients with the buttermilk to your creamed mixture, mixing after each addition.
Finally, when everything is mixed together, fold in the egg whites and mix together, being careful not to over-mix.
Pour the cake batter into a well-greased 9″x13″ cake pan.
Bake at 350° for about 20 minutes, or until a toothpick or cake tester comes out clean.
When the cake is fully baked, remove it from the oven and allow it to fully cool before attempting to frost it. If you’re making round cakes or cupcakes***, let the cakes cool in the pan for about 10 minutes, then remove to a wire rack to finish cooling.
Once the cake has fully cooled, top it with delectable chocolate buttercream frosting****, slice, and serve.