Preheat oven to 350°F (175°C). Grease and flour three 9-inch cake pans.
In a bowl, whisk together flour, cocoa powder, baking soda, and salt.
In a separate bowl, beat butter and sugar until fluffy. Add eggs one at a time, then mix in vanilla.
Alternate adding the dry ingredients and buttermilk, mixing until just combined. Stir in hot water (batter will be thin).
Divide batter evenly among pans. Bake for 30-35 minutes or until a toothpick comes out clean.
Cool cakes in pans for 10 minutes, then transfer to a wire rack to cool completely.
In a saucepan, whisk sugar, evaporated milk, egg yolks, and butter over medium heat.
Cook, stirring constantly, until thickened (about 10-12 minutes).
Remove from heat, stir in vanilla, coconut, and pecans. Let cool to spreadable consistency.
Place one cake layer on a plate, spread half the frosting. Repeat with the second layer and remaining frosting. Top with the third layer.
Heat cream until steaming, pour over chopped chocolate, let sit for 2 minutes, then stir until smooth.
Drizzle over the top of the cake, letting it drip down the sides.
