For the Cake:
Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large bowl, whisk together the flour, baking soda, baking powder, salt, cocoa powder, granulated sugar, and brown sugar.

Add the buttermilk, vegetable oil, eggs, and vanilla extract to the dry ingredients. Mix until smooth and fully combined.

Gradually add the boiling water to the batter, mixing until smooth. The batter will be thin.

Divide the batter evenly between the prepared cake pans and bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

For the Coconut-Pecan Frosting:
In a medium saucepan, combine the granulated sugar, evaporated milk, butter, and beaten egg yolks. Cook over medium heat, stirring constantly, until the mixture thickens (about 10–12 minutes).

Remove from heat and stir in the vanilla extract, shredded coconut, and chopped pecans. Let the frosting cool for about 30 minutes until it thickens further.

Assemble the Cake:
Once the cakes are completely cooled, spread a generous layer of the coconut-pecan frosting on top of the first cake layer. Place the second cake layer on top and frost the top and sides with the remaining frosting.

Slice, serve, and enjoy your delicious German Chocolate Cake!