Preheat oven to 350°F (175°C).

Spray three 9-inch cake pans with nonstick cooking spray with flour.

In a large bowl, beat butter and sugar until fluffy.

Add eggs one at a time, beating well after each addition.

Add sour cream and vanilla, beating until combined.

In a medium bowl, combine flour, cocoa, baking soda, and salt.

Gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture.

Add melted chocolate and beat until combined.

Spoon batter evenly into prepared pans.

Bake for 18 to 22 minutes, or until a wooden pick inserted in the center comes out clean.

Let cool in pans for 10 minutes.

Remove from pans and cool completely on wire racks.

Spread two-thirds of the Coconut-Pecan Filling evenly between 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 Coconut-Pecan Filling evenly over the top of the cake.

Arrange pecan halves around top and bottom of cake if desired.

Garnish with chocolate curls if desired.

Store the cake in the refrigerator.

To make the Coconut-Pecan Filling, combine cream, sugar, and egg yolks in a medium saucepan.

Cook over medium-low heat until sugar is dissolved and the mixture coats the back of a spoon, about 10 minutes.

Remove from the heat and add coconut, pecans, and butter, stirring until the butter is melted.

Let stand until the mixture reaches room temperature.

To make the Chocolate Ganache Frosting, combine the chopped chocolate, butter, and corn syrup in a medium bowl.

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.