Sift together flour, sugar, cocoa, baking soda, baking powder, and saltin a mixing bowl. Add eggs, oil, coffee, buttermilk and vanilla. Beatwith an electric mixer set at medium speed for 3 minutes. Pour batterinto greased 13 x 9 x 2-inch baking pan. Bake in preheated 350 degreeoven for 40 minutes or until the cake tests done. Cool in pan on rack.
Frost with Hundred Dollar Frosting. Cut into squares.
HUNDRED DOLLAR FROSTING:Combine butter and semisweet choclolate in a double boiler top. Placeover hot water, stirring until melted. Remove and cool well. Add egg andstir vigorously. Stir in confectioners' sugar, vanilla and lemon juice.
Beat until smooth. Stir in walnuts and frost cake with icing.