Preheat oven to 350ºF. Cover bottom of 3 (9-inch) pans with wax paper; grease sides of pans.
Microwave chocolate and water in large microwavable bowl for 1 1/2 to 2 minutes or until chocolate is almost melted, stirring after 1 min. Stir until chocolate is completely melted. Cool.
Mix flour, soda, and salt; set aside.
Cream butter and sugar in a large bowl with mixer on medium speed until light and fluffy. Add egg yolks, 1 at a time, beating well after each addition.
Blend in melted chocolate and vanilla.
Add flour mixture alternately with buttermilk, beating until well blended after each addition.
Beat egg whites in a small bowl until stiff peaks forms. Gently stir into batter.
Pour batter evenly into three 9-inch layer pans, lined on bottoms with waxed paper.
Bake for 30 minutes or until until toothpick inserted in centers comes out clean. Immediately run a small metal spatula around cake layers. Cool in pans 15 minutes. Remove layers from pans to wire racks. Discard wax paper. Cool cake layers completely. Spread coconut-pecan frosting between layers and top of cake.
Beat egg yolks, milk and vanilla in large saucepan with wire whisk until well blended. Add sugar and butter; cook on medium heat 12 min. or until thickened and golden brown, stirring constantly. Remove from heat.
Stir in shredded coconut and chopped pecans. Mix well.
Cool until thick enough to spread.