In a medium bowl, whisk together the chocolate, cocoa, and boiling water until smooth; set aside to cool. In another bowl, whisk together the flour, baking soda and salt. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugars until light in color, about 1-2 minutes. Scrape down the bowl with a rubber spatula. Add the eggs one at a time beating well after each addition. Add the cooled chocolate mixture and the vanilla and mix until incorporated. Add the flour mixture in three additions, alternating with sour cream. Mix just until combined.

Evenly pour the batter into the prepared pans. Bake for 20-25 minutes or until a toothpick inserted in the center comes out clean. Cool cakes in the pan for 10 minutes. Invert them on a wire rack to cool completely. (Cooled cakes can be wrapped in plastic wrap and stored at room temperature for 2 days.)

Whisk the milk, cornstarch, butter, brown sugar, and salt in a saucepan over medium-high heat until bubbling, about 3 minutes. Continue to cook until mixture is thickened, about 1 minute. Remove from the heat and stir in the vanilla. Stir in the pecans and coconut and set aside to cool to room temperature.

Heat the water and sugar in a small sauce pan until the sugar is melted. Remove from the heat and add the chocolate liqueur. Set aside to cool.

Place the chocolate, corn syrup, and butter in a medium bowl. Heat the heavy cream to a boil and pour over the chocolate. Let sit for one minute, then stir until smooth and completely melted. Set aside to cool completely. Mixture will thicken as it cools.