Preheat oven to 350°F.
Cover bottoms of either THREE 9-inch round cake pans or TWO 9-inch round cake pans (some batter will be set aside for cupcakes if using TWO pans*) with waxed paper; spray sides with cooking spray.
Microwave chocolate and water in large microwaveable bowl on HIGH for 1-1/2 to 2 min. or until chocolate is almost melted, stirring after 1 min. Stir until chocolate is completely melted.
Mix flour, baking soda and salt. Beat butter and sugar in large bowl with mixer until light and fluffy. Add egg yolks, 1 at a time, beating well after each. Blend in melted chocolate and vanilla. Add flour mixture alternately with buttermilk, beating until well blended after each addition.
Beat egg whites in small bowl with mixer on high speed until stiff peaks form; set aside. Add egg whites to cake batter and gently fold in until blended but do not over mix. Pour into prepared pans. If using three pans, divide batter evenly, if making two layers, place approximately 1/3 of the batter into each pan, and the remaining batter can be used for cupcakes.
Bake for 30-35 minutes or until toothpick inserted in centers comes out clean. Immediately run small spatula around cakes in pans to loosen the cake from the sides to prevent sticking. Cool cakes in pans 15 minutes. Remove from pans and transfer to wire racks. Cool completely prior to frosting with Coconut Pecan Frosting.