Combine chocolate and water, stirring until chocolate, melts; set aside.
Cream butter, gradually add sugar, beating well at medium speed of an electric mixer. Add egg yolks, one at a time, beating well after each addition. Stir in white chocolate mixture and vanilla. Combine flour and soda; add to chocolate mixture alternately with buttermilk, beginning and ending with flour mixture. Beat egg whites (at room temperature) until stiff peaks form; fold into chocolate mixture.
Pour into 3 well greased and floured 9 inch round cake pans. Bake at 350 degrees for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes; remove from pans, and cool completely on wire racks. Spread Coconut-Pecan Frosting between layers on top and sides of cake. Yields one 3 layer cake.