Great recipe! Thank you for doing all the research for us. You certainly have covered all the bases.
I just want to point out that you do not mention at what point you add the mayonnaise.
Just a quick story about this cake from my childhood. My father had lots of imaginary allergies. He just knew that if mayonnaise ever passed his lips he would surely die. After my oldest sister was married, she found the recipe for this cake. Since chocolate cake was his favorite, She brought it to all the family gatherings. He always had seconds and sometimes thirds and never had a second of pain. She got the most unholy glee out of that. She always was kind of a nasty person.
Thank you for this great recipe.