Begin by preparing your pans and melting the chocolate mixture, which forms the foundation of this cake's rich flavor. Grease the bottom of 3 (9-inch) round pans or one 9x13-inch pan to prevent sticking. In a microwave-proof bowl, melt 1 (4-ounce) package of German sweet chocolate with 1/2 cup water on high power for 1 1/2 to 2 minutes, stirring after each minute until the chocolate is completely melted.
While the chocolate cools slightly, combine 2 cups flour, 1 teaspoon baking soda, and 1/4 teaspoon salt in a separate bowl and set aside.
In a large bowl, beat 1 cup butter (2 sticks) and 2 cups sugar together with an electric mixer until the mixture is light and fluffy, typically 2-3 minutes. Add 4 egg yolks one at a time, beating well after each addition to guarantee proper emulsification.
Stir in the cooled chocolate mixture and 1 teaspoon vanilla extract, then alternate adding the flour mixture with 1 cup buttermilk, beating well after each addition. This alternating method prevents overmixing while securing even distribution of ingredients throughout the batter.
In a separate bowl, beat the 4 egg whites until stiff peaks form, then gently fold them into the batter to maintain the airy texture they create. Pour the batter evenly into the prepared pans and bake at 350 degrees for 30 minutes or until a toothpick inserted in the center comes out clean.
Allow the cakes to cool in the pans for 15 minutes before removing them and cooling completely on wire racks. Once cooled, frost with Coconut-Pecan Frosting to complete this classic dessert.