Spray a 9x13 baking pan with nonstick cooking spray.
In a small bowl whisk together flour, cocoa, baking soda baking powder and salt.
In a medium bowl using a hand mixer, beat sugar and eggs until combined. Add in mayonnaise, water, and vanilla and mix until combined.
Add the dry mixture to the wet mixture and mix just until combined.
Pour batter into the baking pan and bake 35-40 minutes or until a toothpick comes out clean.
Let cake cool before frosting.
Ganache Frosting
Heat heavy whipping cream in a medium saucepan on medium-low heat. Once it starts to simmer (about 3-4 minutes) turn off the heat and add chocolate chips and whisk until melted. Add in the butter and whisk until melted.
Let frosting cool completely, then using the hand mixer, mix the frosting until fluffy.