Don’t let the mayo put you off – this is our family’s favorite birthday and every other occasion cake, very moist and devilishly rich ! This cake stores well at room temperature and is great for picnics.
1 Preheat oven to 350 degrees F (175 degrees C). Grease and flour two 9 inch cake pans.
2 Sift together the flour, baking soda, salt, 1 cup white sugar, and 1/2 cup cocoa. Add mayonnaise, 1 teaspoon vanilla, and water. Beat with and electric mixer on medium speed for 3 to 4 minutes. Pour batter into prepared pans.
3 Bake at 350 degrees F (175 degrees C) for 25 minutes. Turn oven off, remove cake layers and allow to cool for 10 minutes in pans. Invert 1 layer onto a serving plate and the other layer onto a cooling rack. Top layer on plate with enough unwrapped mints to fully cover top. Return cake to oven for 3 to 5 minutes to soften chocolate mints, then spread evenly with a spatula. Top with second cake layer and allow to cool before frosting.
4 To Make Fudge Frosting: Combine 6 tablespoons cocoa, 2 cups white sugar, 2/3 cup milk, 1/2 cup butter, and a pinch of salt in a saucepan over medium high heat. Stirring constantly bring mixture to a boil and reduce heat to low, allowing mixture to boil gently for 3 minutes without stirring.
5 Remove from heat and let cool for 3 minutes before beating in 1 teaspoon vanilla extract. Beat with an electric mixer until just barely thick enough to spread without running off the cake. Spread over top of cooled cake.