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1
Preheat oven to 350F.
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2
Butter and flour an angel-food pan.
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3
Cream butter for 4 minutes, beat in mayonnaise, a little at a time, and sugar, a little at at time, and beat for 10 minutes.
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4
Beat in the eggs, one at a time, beating well after each addition and beat for 4 minutes.
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5
With a wooden spoon, stir in chocolate and vanilla.
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6
Into a bowl, sift together flour, soda and salt.
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7
Whisk half the flour mixture and half the milk into the chocolate mixture and whisk in remaining flour and milk.
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8
Pour batter in prepared pan and bake for 50 minutes to 1 hour, or until a tester comes out clean.
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9
Let cake cook in pan for 10 minutes, remove and let cool completely.
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10
Halve cake horizontally.
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11
To make buttercream: Cream butter until light and fluffy, about 4 minutes and beat in 1/3 cup of icing sugar, coffee mixture, salt, half the remaining icing sugar, the cocoa and vanilla.
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12
Beat in remaining icing sugar slowly and beat buttercream at high speed until it is light and fluffy.
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13
Spread a thick layer of buttercream on bottom layer of cake.
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14
Arrange top half on, and spread top and side with a thin layer of remaining buttercream.
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15
Transfer remaining buttercream to a pastry bag and pipe rosettes decoratively around top and base of cake.
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16
Garnish with chocolate shavings.
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17
Chill for 1 hour before serving.
