Preheat oven to 350°F (180°C). Spray 3 (8-inch) round cake pans with baking spray with flour.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugars at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in vanilla.
In a medium bowl, whisk together flour, cocoa, baking powder, baking soda, and salt. With mixer on low speed, gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating just until combined after each addition. Stir in melted chocolate until combined. Divide batter among prepared pans (about 2 cups or 570 grams each), smoothing tops with an offset spatula.
Bake until a wooden pick inserted in center comes out clean, 30 to 35 minutes. Let cool in pans for 10 minutes. Remove from pans, and let cool completely on wire racks.
Place 1 cooled cake layer on a cake plate. Spread 2 cups (498 grams) Coconut-Pecan Frosting on top. Top with second cake layer, and spread 2 cups (498 grams) frosting on top. Top with remaining cake layer, and spread remaining Coconut-Pecan Frosting on top and sides of cake.
