Instructions: Grease 13 x 9" metal pan.

In a large bowl, combine flour, sugar, cocoa, baking soda and salt.

In a medium bowl with a wire whisk mix buttermilk, mayonnaise, vanilla and eggs until almost smooth. With spoon stir buttermilk mixture into flour mixture until batter is smooth. Spoon batter into baking pan.

Bake at 350 F. for 35-40 minutes until toothpick inserted in center of cake comes out clean. Cool cake in pan on wire rack.

Frosting: In heavy small saucepan, melt semisweet chocolate and unsweetened chocolate over a low heat. Remove saucepan from heat, cool chocolate to room temperature. In a large bowl with mixer at low speed, beat powdered sugar, margarine, and vanilla until almost combined. Add melted cooled chocolate; increase speed to high and beat about 1 minute until fluffy and light.

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