• Preheat your oven to 350F, and grease and line two 8" cake pans. With your two oranges, zest them into a bowl and set aside. In a separate bowl, squeeze the juice from the oranges and then add to your bowl of zest. Add the following ingredients to the bowl through a strainer: flour, cocoa powder,  and baking powder. Mix well.

  Now, add the sugar, salt, milk, vegetable oil, eggs, and vanilla extract. Mix well until you have a smooth batter and the ingredients are combined. Finally, stir in the hot water.
• Pour your batter evenly into the two prepared cake pans. In the case, you want to make a 4-layer cake, split the batter in 4.  Place your cakes into the oven's center and bake for 30-40 minutes. When your cakes are baked, a toothpick into the center of the cake should come out clean.

Prepare the orange custard for the filling

• In a saucepan add milk and the zest of the orange. Mix gently with a whisk, and add two tablespoons of the sugar, along with the vanilla extract. Place on low heat and slowly heat.
• In a mixing bowl, add the egg yolks, the remainder of the sugar, cornstarch, and flour. Mix well. Once the milk mixture begins to feel warm, gradually pour it into the egg yolk mixture; whisking as you go. Continue adding in small increments until all the milk is incorporated into the egg yolks.
• Once all the milk is added, pour the entire mixture back into the saucepan and continue to heat, whisking constantly until the mixture thickens. Whisk the custard the whole time and don't step away. Stop heating when the custard can coat the back of a spoon and your finger leaves a trail there.
• Once thickened, pass through a sieve to remove any lumps. Melt your chocolate into a microwave-safe bowl and then add the chocolate to your custard and mix. Then cover with plastic wrap and chill for around 2 hours or so.

Finish orange filling

• After the custard is chilled, in a medium bowl add your softened butter and confectioners' sugar to a stand mixer and beat until fluffy. Add around 2 tablespoons of fresh orange juice and the cocoa powder; mix completely. Gradually add small increments of the chilled custard; whipping as you go. It should be smooth and thick.

Make the dark chocolate and orange ganache

• In a small saucepan, add the whipping cream, along with the zest, and peel. Heat on low heat until it starts to bubble. Pour the cream through a sieve into your bowl of chocolate. Stir it together until everything is glossy and all the chocolate has melted. Leave to cool and then stir until smooth.

Assemble the cake

• Cut your cakes in half horizontally so you have four cake layers. Add one to your cake plate and add a layer of the filling. Smooth the filling and then add the next cake layer on top. Repeat until all layers are assembled. Then add a thin layer around the sides of the top.
• Pour the ganache over the top of your frosted cake so it drips down the sides. Leave at room temperature to set. Slice, serve, and enjoy!