Melt chocolate in 1/2 cup boiling water. Cool. Cream butter and sugar until light and fluffy. Add egg yolks, one at a time, and beat well after each. Add the melted chocolate and vanilla. Mix well.
Sift together the salt, baking soda, and flour. Then add alternately with buttermilk to chocolate mixture, beating well. Beat until batter is smooth.
Beat egg whites until stiff peaks form. Fold into batter. Pour into three 8 or 9-inch cake layer pans, lined on bottoms with wax paper. Bake in moderate oven (350°F) 35 to 40 minutes. Cool. Frost tops only with Coconut Pecan Frosting or use any favorite frosting or whipped cream.