For the icing: Combine the chocolate chips and corn syrup in a large heatproof bowl. Bring the heavy cream and espresso powder to a simmer in a small saucepan over medium heat (do not boil). Pour the hot cream over the chocolate and let stand 2 minutes before whisking until smooth. If the chocolate is not completely melted, heat in the microwave in 10 second intervals, stirring, until melted. Stir in the vanilla, and then cool to room temperature, about 1 hour. Beat in the butter until fully incorporated using a hand mixer. The icing should be smooth and shiny.
For the filling: Whisk the sugar, salt and egg yolks in a large saucepan until combined. Mix in the butter with a wooden spoon, and then whisk in the heavy cream. Cook over medium heat until the mixture thickens and coats the back of a spoon, 8 to 10 minutes, whisking frequently. Pour the mixture through a fine-mesh sieve into a large bowl and stir in the bourbon and vanilla. Cool to room temperature, and then stir in the coconut and pecans.
For the cake: Preheat the oven to 350 degrees F. Spray two 9-inch round baking pans with cooking spray and line with parchment paper. Spray the paper and set aside.
Combine the butter, chocolate and espresso powder in a heatproof bowl set over a pot of barely simmering water. Stir until melted and smooth, and then remove from the heat and let cool 5 minutes.
Sift the flour, cocoa powder, baking powder, baking soda and salt into a large bowl.
Mix the sugar and melted chocolate mixture in the bowl of an electric mixer on medium speed until combined, about 1 minute. Mix in the vanilla, and then add the eggs one at a time, mixing after each addition and scraping the bowl as needed. Reduce the speed to low and add the flour mixture alternately with the buttermilk, beginning and ending with the flour mixture. Mix until combined, and then increase the speed to medium and beat 30 seconds.
Divide the batter evenly between the prepared pans and smooth with an offset spatula. Bake until a toothpick inserted into the center comes out clean, 40 to 45 minutes. Cool the cakes in the pans on wire racks 15 minutes, and then remove the cakes and cool completely.
For assembling the cake: Halve one cake layer horizontally to make 2 cake layers, and place the top layer cut-side up on a cake plate. Spread one-quarter of the filling over the cut side, and then top with the other half of the cake, cut-side down. Spread another one-quarter of the filling over the cake. Repeat the process with the remaining cake and filling. You should still have one-quarter of the filling remaining.
Spread the icing on the top and around the sides of the cake, reserving about 2/3 cup for garnish. Pipe a decorative border around the top of the cake using a piping bag fitted with a star tip, and then fill in the border by spreading the remaining pecan-coconut filling on top of the cake. Refrigerate 1 hour before serving.
Store the cake in a container in the refrigerator up to 7 days.