Set oven to 350˚F. Grease baking pans with butter, or spray with cooking spray, then dust lightly with flour.*
In 2 cup measuring cup, add vinegar then fill to the 2 cup line with milk. Stir. It will begin to look appear curdled, but that is ok. Set aside.
In a large stand mixer bowl, add boxed chocolate cake mix, flour, sugar, cocoa, espresso powder. Whisk to combine.
Add in the soured milk mixture, eggs, melted butter and vanilla. Mix on low until just incorporated, then scrape down the sides.
Mix on medium speed for 2 minutes, then divide evenly into prepared pans.
Bake for 25 minutes, or until toothpick inserted comes out clean.
Set on wire baking rack to cool completely.
German Chocolate Cake Topping
In a medium saucepan, add brown sugar, butter, egg yolks, and evaporated milk. Stir to combine and bring the mixture to a low boil over medium heat. Stir constantly for several minutes until the mixture begins to thicken.
Remove from heat and stir in vanilla, nuts and coconut. Allow to cool completely before layering it on the cake.
Chocolate Frosting
In a large stand mixer bowl, add softened butter, cocoa, espresso powder and 1 cup of the powdered sugar. Blend slowly until incorporated. Mix in the vanilla and condensed milk and whisk on medium speed.
Continue adding in the powdered sugar ½ cup at a time until frosting is smooth and to your desired consistency, and to your taste for sweetness. Add more powdered sugar and/or milk to achieve desired consistency.
Assembly
Place one cake on a serving platter or plate.
Using a piping bag, or zippered bag with a corner snipped, pipe a thick chocolate frosting rim around the edge of the cake. Fill the middle with coconut pecan topping.
Place second cake on top. Pipe chocolate frosting around the top of the cake and frost the sides. Fold the remaining topping into the center. Decorate with additional chocolate frosting as desired.
Notes
*My preference is to line the bottom of each baking pan with parchment. Spray bottom on pan lightly, lay parchment cut to the size of the pan on top of greased layer, spray again and dust with flour. Tap pan to distribute flour.
Use a weigh scale to distribute the cake batter between pans for more even baking.