Melt sweet baking chocolate in boiling water and stir until smooth.

Cool the melted chocolate and set aside.

Cream margarine and slowly add sugar, beating well with an electric mixer.

Add egg yolks one at a time, beating well after each addition.

Add the cooled chocolate and vanilla, beating until blended.

Sift together cake flour, salt, and baking soda.

Gradually add the sifted dry ingredients to the egg mixture, alternating with buttermilk.

Beat egg whites at room temperature until stiff peaks form.

Gently fold the beaten egg whites into the batter.

Grease and flour three 9-inch round cake pans.

Pour equal amounts of batter into each cake pan.

Bake at 350°F (175°C) for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.

Cool in the pans for 10 minutes before removing.

Remove the cakes from the pans and let them cool completely on wire racks.

Spread with Coconut-Pecan Frosting.