Preheat oven to 375°. Grease a 9- x 2-inch cake pan, line the bottom with parchment paper, and set aside.
Combine bourbon and sugar in a large saucepan; bring mixture to a boil. Remove from heat, and add chocolate and butter, stirring until smooth. Set aside, and let cool to room temperature.
Beat in eggs, one at a time, until very well blended. Fold in flour and 1 1/2 tablespoons cocoa powder. Pour batter into prepared cake pan. Set pan in a large roasting pan filled to depth of 1 inch with hot water.
Bake at 375° for 1 hour and 15 minutes, basting with Coffee-Bourbon Syrup every 15 minutes after a crust has developed on cake's surface.
Cool cake; cover and refrigerate 6 hours or overnight. Transfer cake onto a serving plate, and dust with remaining 1 tablespoon cocoa powder. Top with hazelnuts.