Preheat the oven to 375°F. Put oil in two baking pans that are 8 or 9 inches in diameter. I like to cut a circular piece of wax or parchment paper for the bottom of the pan to help the cake come out easily.
About the Cake:
Mix sugar, flour, cocoa, baking powder, baking soda, and salt in a big bowl. In another bowl, mix the eggs, buttermilk, oil, and vanilla until well combined. Combine the liquid ingredients with the dry ones and mix them together. Add hot water (the mixture will become very liquid). Put the batter into the pans that have been prepared.
Bake for 25 to 35 minutes, adjusting the time according to the size of your cake pan. The 9-inch pan bakes faster. Bake until a toothpick inserted in the center comes out clean or with a few crumbs. Let it cool for 5 minutes in the pan, then flip it onto wire racks to cool completely.
To make the frosting for German Chocolate Cake:
In a pot, put brown sugar, white sugar, butter, egg yolks, and evaporated milk. Mix well and heat the mixture until it starts to boil gently on medium heat. Keep stirring continuously for a few minutes until the mixture starts to thicken.
Take off the heat and mix in vanilla, nuts, and coconut. Let it cool down completely before putting it on the cake.
To make the chocolate buttercream frosting:
Heat the butter until it becomes liquid. Add cocoa powder and mix. Add powdered sugar and milk little by little, mixing until you reach a smooth and spreadable texture. Add a little more milk or powdered sugar as needed until the frosting is the thickness you want. Add vanilla extract and mix.
Putting together a cake:
Put one of the cake layers on your serving dish or plate.
Spread a thin layer of chocolate frosting on the cake, then put half of the coconut frosting on top and spread it evenly. Leave a small space, approximately half an inch, between the filling and the edge of the cake.
Put the second cake layer on top. Spread chocolate icing on the whole cake.
Put the rest of the coconut frosting on the cake.