Start by preheating your oven to 350°F (175°C). Grease the three 8-inch cake pans thoroughly and line the bottoms with parchment paper to ensure the cakes release easily once baked. This step is pivotal to avoid sticking and to keep your cake layers perfectly intact.

In a large mixing bowl, whisk together the flour, cocoa powder, baking soda, and salt. Ensuring these dry ingredients are evenly combined will help guarantee an even distribution of flavor and proper rise during baking.

Using an electric hand or stand mixer, cream the butter and sugar together in a separate bowl until the mixture becomes light and fluffy. This process incorporates air into the batter, resulting in a light and tender cake texture. Add the vanilla extract to enhance the flavor profile.

Add the eggs to the creamed butter and sugar mixture one at a time, beating well after each addition. This step allows the eggs to combine properly with the batter, ensuring a smooth and consistent texture for your cake.

Gradually incorporate the dry ingredients into the wet batter, alternating with the addition of buttermilk. Begin and end with the dry ingredients, mixing them in just until combined. Overmixing should be avoided to maintain the cake's soft and fluffy crumb.

Gently fold the shredded coconut and chopped pecans into the batter using a spatula. This not only adds texture but also infuses a delightful crunch and natural sweetness into the cake layers.

Divide the batter evenly among the prepared cake pans, using a spatula to level the tops. Bake the cakes in the preheated oven for approximately 25-30 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool slightly in their pans before transferring them onto a cooling rack.

While the cakes are cooling, prepare the frosting in a saucepan. Combine condensed milk, egg yolks, butter, and vanilla extract, cooking over medium heat while stirring constantly until the mixture thickens. Remove from heat and stir in shredded coconut and pecans, allowing the frosting to cool before use.

Place one cake layer on a serving plate or stand. Spread an even layer of frosting on top before adding the next cake layer. Repeat this process until all layers are stacked and frosted. Use an offset spatula to spread the remaining frosting over the top and sides of the cake. If desired, garnish with white chocolate shavings or whole pecans for a decorative finish.

Allow the assembled cake to set in the refrigerator for at least 30 minutes before serving. This step helps the layers hold together and enhances the overall flavor. Slice, serve, and enjoy your decadent White German Chocolate Cake!