Step 1: Preheat oven to 350°F (175°C). Grease and flour 3 (9-inch) round cake pans. Line the bottoms with parchment paper.
Step 2: Melt the German's sweet chocolate either in a microwave in 30-second intervals or over a double boiler. Set aside to cool slightly.
Step 3: In a medium bowl, whisk together the flour, baking soda, and salt.
Step 4: In a large mixing bowl, cream together the softened butter and 2 cups granulated sugar until light and fluffy.
Step 5: Beat in the 4 egg yolks one at a time, mixing well after each addition. Stir in 1 teaspoon vanilla extract.
Step 6: Gradually add the dry ingredients alternately with the buttermilk to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.
Step 7: Stir in the cooled melted chocolate, then carefully fold in the ½ cup boiling water until just incorporated. Do not overmix.
Step 8: In a separate clean bowl, beat the 4 egg whites until stiff peaks form. Gently fold the beaten egg whites into the cake batter until no streaks remain.
Step 9: Divide the batter evenly among the three prepared cake pans. Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean.
Step 10: Let the cake layers cool in their pans on a wire rack for 10 minutes before inverting them onto the wire racks to cool completely.
Step 11: For the Coconut-Pecan Frosting: In a medium saucepan, whisk together the evaporated milk, 1 cup granulated sugar, 4 egg yolks, and ½ cup cubed butter. Cook over medium-low heat, stirring constantly, for 10-12 minutes, or until the mixture thickens to a custard-like consistency. Do not boil.
Step 12: Remove the frosting mixture from the heat and stir in 1 teaspoon vanilla extract, shredded coconut, and chopped pecans. Let the frosting cool completely at room temperature, stirring occasionally, until it is thick enough to spread.
Step 13: Once the cake layers are completely cool, place one layer on a serving plate or cake stand. Spread about one-third of the coconut-pecan frosting over the top. Repeat with the second and third layers. Spread any remaining frosting around the sides of the cake.
Step 14: Slice and serve your decadent German Chocolate Cake. Enjoy!