Prep the pans: Heat oven to 350°F (175°C).
Grease and line two 9-inch round cake pans with parchment. Lightly flour the sides.
Bloom the chocolate: Place the chopped dark chocolate in a heatproof bowl. Pour the hot coffee over it and let sit 2 minutes.
Stir until smooth. Set aside to cool slightly.
Mix dry ingredients: In a large bowl, whisk flour, cocoa, sugar, baking powder, baking soda, and salt until combined.
Combine wet ingredients: In another bowl, whisk eggs, buttermilk, oil, and vanilla until smooth. Whisk in the melted chocolate-coffee mixture.
Make the batter: Pour wet into dry and whisk gently until just smooth.
The batter will be thin—this is good for a moist cake.
Bake: Divide batter evenly between pans. Bake 26–32 minutes, until a toothpick comes out with a few moist crumbs. Cool in pans 10 minutes, then turn out onto racks to cool completely.
Toast pecans: While the cakes bake, toast pecans on a sheet pan for 7–9 minutes at 350°F, until fragrant.
Cool, then chop.
Cook the frosting base: In a medium saucepan, whisk evaporated milk, egg yolks, granulated sugar, brown sugar, and butter. Cook over medium heat, stirring constantly, until thickened and glossy, 8–10 minutes. Do not boil hard.
Finish the frosting: Remove from heat.
Stir in vanilla, salt, coconut, and pecans. Let cool to room temperature; it will thicken as it cools.
Optional ganache: Warm cream to steaming, pour over chopped chocolate with a pinch of salt, and let sit 2 minutes. Stir until smooth; cool until spreadable.
Assemble: Level cake layers if needed.
Place the first layer on a plate. If using, spread a thin layer of ganache, then half the coconut-pecan frosting. Top with second layer and finish with remaining frosting.
Leave the sides semi-naked or add more frosting if you reserved some.
Set and serve: Chill 20–30 minutes to set clean slices. Serve at room temperature for best texture.