Preheat the oven to 275℉.
Coat the bottom and sides of a 9-inch spring-form pan with butter. Line the bottom of the pan with parchment paper.
Using a vegetable peeler, remove the outer zest of the orange in long strips. Set aside.
Juice the orange.Measure 3 tbsp of orange juice into a medium sauce pan.Add the remaining orange juice to a measuring cup. Add the bourbon to the remaining orange juice. Then, add enough water in the measuring cup to equal 1 cup of total liquid. Set aside. In the sauce pan, add the sugar. Add the orange zest strips. Set over medium-high heat and cook until the sugar has dissolved. Note: Do not stir, but swirl the pan. It will help to distribute the heat evenly and prevent sticking.Continue cooking until the sugar caramelizes to a deep golden brown color. Remove the pan from the heat and carefully pour the orange juice-bourbon concoction; the caramel will bubble up and harden. Set the pan over medium heat, bring to a simmer and cook, stirring until the caramel has fully dissolved. Once the caramel has dissolved, remove from the heat and stir in the amaro. Over a double boiler, melt the chocolate. Add the butter and stir until the butter is fully melted. Stir in the instant coffee powder. Set aside.
Immediately pour the caramel syrup through a strainer into the melted chocolate. Reserve the orange strips.
Using a silicone spatula, gently stir the mixture, without incorporating air, until well combined.
Add the beaten eggs to the chocolate mixture and stir using the silicone spatula, until homogenous and glossy.
Pour the batter into the prepared spring-form pan. Gently tap the sides of the pan to remove any air bubbles. If needed, use a spoon to smooth the top.
Set the pan on a wire rack over a baking sheet. Bake until the cake barely jiggles (about 45 minutes).
Remove the cake from the oven and run a thin knife around the edges to loosen the sides of the cake from the pan. Cool to room temperature in the pan.When the cake has cooled, remove it from the springform pan. Refrigerate uncovered overnight, or at least 4 hours. Transfer the zest strips to a bowl, sprinkle with granulated sugar and toss until the strips are fully coated. Cover and store at room temperature overnight, or at least 4 hours.When ready, remove the zest strips from the sugar and cut them into thin strips to decorate the cake.Dust the cake with the sugar used to coat the zest strips. Then, arrange the strips around the edges on the cake. Remove the cake from the fridge 1 hour before serving. Slice the cake using a knife ran under hot water. Wipe the knife between every slice.Serve and enjoy!
