Mississippi Mud Cake/Pie (Tennessee, 1976?)

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   DARE has nothing at all.  OED (Jesse has just told me) has 1990.
   A bit of checking around the old studio apartment here has turned up:

THE NASHVILLE COOKBOOK:
SPECIALTIES OF THE CUMBERLAND REGION
By Nashville Area Home Economics Association
1976, 1977
(See catnyp.nypl.org for full cite)
Cakes:
Mississippi Mud, 161

   So, based on my investigation, the Mississippi Mud Cake/Pie possibly comes from Tennessee, possibly from a secret recipe of Bethany Dumas.