1. Preheat oven to 350°. Grease and lightly flour two 9-inch round cake pans*; set aside.
2. In medium bowl, combine flour, cocoa, baking soda and baking powder; set aside.
3. In large bowl, with electric mixer at high speed, beat eggs, sugar and vanilla for 3 minutes or until light and fluffy. Beat in Hellmann's® or Best Foods® Mayonnaise at low speed until blended. Beat in flour and water mixture & pour into prepared pans.
4. Bake 30 minutes or until toothpick inserted in centers comes out clean. On wire racks, cool 10 minutes; remove from pans and cool completely. Frost, if desired, or sprinkle with confectioners' sugar. (3/9/18: took 35 minutes to bake w/ 2X 9 in.)