MAKE THE GERMAN CHOCOLATE CAKE LAYERS: Preheat the oven to 350 degrees F. Butter three 8-inch cake pans, line the bottoms with parchment paper, and butter the parchment. Dust with flour, and knock out the excess flour.
Sift the cake flour, cocoa powder, baking powder, baking soda, and salt into a medium mixing bowl. In a small bowl, whisk together the coffee and buttermilk.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and sugar until fluffy. Scrape down the bowl and add the eggs, one at a time, beating until each is incorporated. Add the vanilla and beat to incorporate. The mixture will look light and fluffy.
Add the flour mixture, alternating with the coffee/buttermilk mixture, in three additions, beginning and ending with the flour mixture. Remove the bowl from the mixer and fold in the melted chocolate.
Divide the batter among the prepared pans and smooth the tops. Bake for 30 to 35 minutes, rotating the pans halfway through the baking time, until a toothpick inserted in the center of each cake comes out clean. Transfer the cakes to a wire rack and let cool for 20 minutes. Invert the cakes onto the rack and remove the pans and let cool completely. Remove the parchment.
MAKE THE COCONUT PECAN FILLING: Preheat the oven to 300 degrees F. Line a baking sheet with parchment paper.
Spread half of the coconut evenly across the pan and place in the oven for 5 minutes or until the coconut begins to brown. Remove from the oven and cool on a wire rack.
In a large saucepan, stir together the sugar, butter, evaporated milk, vanilla, and egg yolks. Bring the mixture to a boil, stirring constantly. After the mixture begins to boil and thicken, remove from the heat and stir in the toasted coconut, regular coconut, and pecans.
Place the pan over an ice bath (a large bowl filled with ice) and stir the mixture until cool.
ASSEMBLE THE CAKE: Place one cake layer on a serving platter. Trim the top to create a flat surface and evenly spread one third of the filling on top. Add the next layer, trim and frost with one third of the filling, then add the third layer. Trim the top, and frost with the remaining filling. The cake will keep in an airtight container, at room temperature, for up to 2 days.