In a medium saucepan, whisk the egg yolks and evaporated milk together. Add the sugars, butter, and salt and cook over medium heat, whisking constantly until the mixture is boiling and thickened. The consistency should coat the back of a spoon like a thin pudding.

Remove the pan from the heat and stir in the vanilla, coconut, and pecans. Allow filling to cool completely before filling the cake.

In a double boiler, combine the chocolate, cocoa powder, hot water, and espresso powder, stirring until smooth. Mixture will be thick. Remove from heat and set aside to cool.

In a medium bowl, whisk together the flour, baking soda, and salt.

In a stand mixer fitted with the paddle attachment, beat the butter and sugars on high until light and fluffy, about 3 minutes. Reduce the speed to medium and add the eggs and egg yolk one at a time, beating well after each addition and scraping down the sides of the bowl as needed. Add the chocolate mixture and vanilla and continue beating until combined.

Add 1/3 of the flour mixture followed by 1/2 of the yogurt, mixing until incorporated. Repeat process with remaining flour mixture and yogurt until batter is thoroughly combined. Scrape down the sides of the bowl and give one last stir before dividing batter equally among the prepared pans, smoothing the tops with a spatula. Lightly tap pans against the countertop to settle any batter and to eliminate any air bubbles.

Bake for 27-30 minutes, or until a toothpick inserted in the center comes out with few crumbs attached. Cool in the pan for 10 minutes, then transfer the cakes to a wire rack to cool completely.

Place the chocolate in a microwave-safe bowl and heat in the microwave until smooth. Allow to cool to almost room temperature. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium speed until creamy.

Add the powdered sugar, a 1/2 cup at a time, beating until smooth. Scrape down the sides of the bowl, then add the melted chocolate, vanilla, and salt. Beat on high until buttercream is light and fluffy, about 2 minutes.

Slice each cake layer in half horizontally, so that you end up with 4 even cake layers. Place one cake layer on a plate or cake pedestal and spread with 1/4 of the coconut-pecan filling. Repeat, alternating layers of cake and filling, ending with a layer of filling. Using an offset spatula or a butter knife, frost the sides of the cake. Place the rest in a pastry bag fitted with a tip, and decorate as desired. Store in the refrigerator until ready to serve.