Preheat the oven to 350 degrees F. Spray three 9-inch cake pans with nonstick cooking spray with flour.
In a large bowl, beat the butter and sugar at medium-high speed with an electric mixer until fluffy. Add the eggs, one at a time, beating well after each addition. Add the sour cream and vanilla, beating until combined.
In a medium bowl, combine the flour, cocoa, baking soda and salt. Gradually add to the butter mixture, alternately with the buttermilk, beginning and ending with the flour mixture. Add the melted chocolate, beating until combined.
Spoon the batter evenly into the prepared pans. Bake until a wooden pick inserted in the center comes out clean, 18 to 22 minutes. Let cool in the pans for 10 minutes. Remove from the pans and cool completely on wire racks.
Spread two-thirds of the Coconut-Pecan Filling evenly in between the cake layers. Place the cake in the freezer for at least 1 hour.
Spread Chocolate Ganache Frosting evenly over the top and sides of the cake. Spread the remaining one-third Coconut-Pecan Filling evenly over the top of the cake. Arrange the pecan halves around top and bottom of cake if desired. Garnish with chocolate curls if desired. Store the cake in the refrigerator.
In a medium saucepan, combine the cream, sugar and egg yolks. Cook over medium-low heat until the sugar is dissolved and the mixture coats the back of a spoon, about 10 minutes. Remove from the heat and add the coconut, pecans and butter, stirring until the butter is melted. Let stand until the mixture reaches room temperature.
In a medium bowl, combine the chopped chocolate, butter and corn syrup. Pour the boiling cream over the chocolate mixture. Let stand for 1 minute. Stir until the chocolate is melted and the mixture is smooth. Chill for 30 minutes, stirring occasionally, until the frosting is a spreadable consistency.