Make the Cake:

1. Preheat the oven to 350°F (175°C). Grease and flour three 9-inch round cake pans, lining the bottoms with parchment paper for easy removal.
2. Melt the Chocolate: In a small bowl, pour the boiling water over the German sweet chocolate, stirring until the chocolate is completely melted. Set aside to cool.
3. Dry Ingredients: In another bowl, whisk together the flour, baking soda, and salt.
4. Cream Butter and Sugar: In a large mixing bowl, beat the softened butter with the granulated sugar until light and fluffy. Add the egg yolks, one at a time, beating well after each addition. Stir in the vanilla extract and the melted chocolate.
5. Alternate Dry and Wet Ingredients: Alternately add the dry ingredients and buttermilk to the creamed mixture, starting and ending with the dry ingredients. Mix until just combined.
6. Beat Egg Whites: In a separate bowl, beat the egg whites until stiff peaks form. Gently fold the egg whites into the batter.
7. Bake: Divide the batter evenly among the prepared pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Cool the cakes in the pans for 10 minutes, then transfer to wire racks to cool completely.

Make the Coconut-Pecan Frosting:

1. Cook the Frosting: In a medium saucepan, combine the evaporated milk, granulated sugar, egg yolks, and butter. Cook over medium heat, stirring constantly, until the mixture has thickened, about 12 minutes. Remove from heat.
2. Add Coconut and Pecans: Stir in the vanilla extract, shredded coconut, and chopped pecans. Let the frosting cool until it reaches a spreadable consistency.

Assemble the Cake:

1. Layer the Cake: Place one cake layer on a serving plate. Spread a third of the frosting over the top. Repeat with the remaining cake layers and frosting, spreading the frosting on top of each layer.
2. Decorate: If desired, pipe additional frosting around the edges for decoration or sprinkle with some toasted coconut or chopped pecans.