Preheat and Prep: Heat your oven to 375°F. Grease two 8 or 9-inch round baking pans and line the bottoms with parchment paper.

Mix Dry Ingredients: In a large mixing bowl, whisk together the granulated sugar, flour, cocoa powder, baking powder, baking soda, and salt.

Add Wet Ingredients: In a separate medium bowl, whisk the eggs, buttermilk, oil, and vanilla extract until smooth. Pour the wet mixture into the dry ingredients and mix until just combined.

Bloom the Cocoa: Carefully pour the boiling water into the batter and gently stir until smooth. The batter will be very thin.

Bake: Divide the batter evenly between the prepared cake pans. Bake for 25 to 35 minutes, or until a toothpick inserted into the center comes out clean. Cool in the pans for 5 minutes, then invert onto wire racks to cool completely.

Cook the Coconut-Pecan Custard: In a medium saucepan, combine the brown sugar, granulated sugar, ½ cup butter, egg yolks, and ¾ cup evaporated milk. Bring to a low boil over medium heat, stirring constantly until the mixture begins to thicken (about 3-5 minutes).

Finish the Filling: Remove from heat. Stir in the vanilla extract, chopped pecans, and shredded coconut. Set aside to cool completely and thicken.

Make the Chocolate Buttercream: Melt the remaining ½ cup of butter. Stir in the ⅔ cup cocoa powder to form a thick paste. Alternately add the powdered sugar and ⅓ cup evaporated milk, beating until smooth and spreadable. Stir in 1 teaspoon of vanilla extract.

Assemble the Cake: Place one cooled cake layer on a serving plate. Spread a thin layer of chocolate frosting over the top, then spoon half of the cooled coconut-pecan filling into the center, leaving a ½-inch border.

Final Frosting: Top with the second cake layer. Frost the sides and the outer top edge of the cake with the remaining chocolate buttercream. Spoon the remaining coconut-pecan filling into the center of the top layer. Slice and serve!