Cover bottoms of 3 (9 inch round cake pans) with waxed paper (I just spray and flour bottoms and sides of cake pans) Spray sides with cooking spray. Microwave chocolate and water in large microwaveable bowl on high 1 1/2 - 2 minutes or until chocolate is almost melted, stirring after 1 minute. Stir until chocolate is completely melted.
Beat egg whites in small bowl with mixer on high speed until stiff peaks form; set aside. 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 misture alternately with buttermilk, beating until well blended after each addition.
Add egg whites; stir gently until well blended. Pour into prepared pans.
Bake 30 minutes or until toothpick inserted in centers comes out clean. Immediately run small spatula around cakes in pans. Cool cakes in pans 15 minutes; remove from pans to wire racks. Cool completely. Spread Coconut-Pecan Filling and Frosting between cake layers and onto top of cake.
Beat egg yolks, milk and vanilla in large saucepan with whisk until well blended. Add sugar and butter, cook on medium heat 12 minutes or until thickened and golden brown, stirring constantly. Remove from heat.