I have found this to be a very moist chocolate cake very similar my grandmother used to make. She used only mayonnaise, but I have found adding sour cream really makes a great cake when mixed with mayonnaise.
Grease large cake pan or multiple smaller pans (ie 9 x 1 ½” layer pans). If you don’t use Demarle Bakeware then grease and flour the bottom of your pans.
Sift dry ingredients together into a large bowl. Stir in Mayonnaise and sour cream and eggs. Gradually stir in water and vanilla and blend until smooth.
Bake at 350 degrees for about 30 minutes or until cake springs back when touched, don’t over bake. When your tester comes clean remove cake immediately. Cool completely. Remove from pan.
Blend all ingredients together in either a mixer or with a hand mixer.
If you just want sour cream frosting without the chocolate add the difference of the ⅓ c to your sugar.