Preheat oven to 350 degrees F (175 degrees C). Line bottom of 9×13 pan with parchment paper.
Microwave chocolate and water on high for 1 1/2 to 2 minutes. Stir halfway through. Stir until all is melted and smooth.
In a medium bowl, mix together flour, soda and salt. Set aside.
In a large bowl, cream 1 cup butter and 2 cups sugar until light and fluffy. Add 4 egg yolks one at a time, beating well after each addition. Stir in chocolate and 1 teaspoon vanilla. Add flour mixture alternately with buttermilk. Beat after each addition until smooth.
In a separate bowl, beat egg whites on high until soft peaks form. Gently fold into batter. Pour into 9×13 inch pan.
Bake at 350 degrees F (175 degrees C) for 30 minutes, or until toothpick inserted into center of cake comes out clean. Cool completely, then frost with coconut-pecan frosting.
Combine milk, 1 1/2 cup sugar, 3/4 cup butter, 4 egg yolks and 1 1/2 teaspoons vanilla in large saucepan. Cook and stir on medium heat for about 12 minutes, or until thick and golden brown. Remove from heat. Stir in coconut and pecans. Cool to room temperature, and spreading consistency.
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