Preheat oven to 350 degrees F.
In a large bowl combine Pillsbury Purely Simple Chocolate Cake and Cupcake Mix, mayonnaise and three eggs. If using espresso powder, dissolve into 1 cup water, and add to the mix, otherwise simply add one cup of water to the mix.
Stir to combine than mix with an electric mixer for two minutes.
Pour into two 8" round cake pans that have been coated with non-stick cooking spray.
Bake for approximately 30-35 minutes or until a toothpick inserted into the center of cakes comes out clean.
Remove from oven and allow to cool for five minutes, then invert cakes from pans and onto wire cooling rack. Allow to cool completely.