Preheat oven to 350°F (175°C). Grease and flour three 9-inch round cake pans.
Pour boiling water over chocolate, stirring until melted. Let cool.
Cream butter and sugar until fluffy. Add egg yolks, one at a time, beating well after each. Stir in vanilla and chocolate.
Sift flour, baking soda, and salt together. Add alternately with buttermilk to chocolate mixture, beginning and ending with flour mixture.
Beat egg whites until stiff peaks form. Fold into batter.
Pour batter into prepared pans. Bake for 30 minutes or until a toothpick inserted in the center comes out clean. Cool in pans for 10 minutes, then remove to wire racks to cool completely.
For frosting: Combine evaporated milk, sugar, egg yolks, butter, and vanilla in a saucepan. Cook over medium heat, stirring constantly, until thickened. Remove from heat. Stir in coconut and pecans. Cool until spreadable.
Spread frosting between layers and on top of cake.