Begin by preheating the oven to 325 F / 165 C. Line three 8-inch pans with parchment rounds and spray with non-stick baking spray. Set aside.

Add 1 cup unsalted butter and 2 1/2 cups of sugar into the bowl of a stand mixer and mix on high for 1 minute with a whisk attachment or a hand mixer. The mixture should become light in color.

Mix in 4 large eggs, two at a time. Mix on medium high until they're fully incorporated.

In a separate bowl, combine the 1 cup orange juice, 1 cup of buttermilk, 1 cup of black cocoa, 2 Tbsp of fresh orange zest, and 2 tsp orange emulsion or extract. Whisk until no clumps remain.

Next, mix 1 cup of self-rising cake flour into the butter/egg mixture on a low speed. Scrape the sides of the bowl with a rubber spatula to make sure the flour gets fully mixed in.

Pour in half of the orange juice/cocoa mixture and gently pulse the mixture at first to incorporate the liquid (if you don't, you'll end up splattering the cocoa mixture all over your kitchen!). Then mix on low until incorporated.

Repeat with another cup of cake flour followed by the remaining orange juice/cocoa mixture, scraping the sides of the bowl as needed.

Add in the 3rd cup of self-rising cake flour and mix on low until the flour is just incorporated. Scrape the sides as needed. You want to be careful not to over-mix the batter or else you'll end up with dense cake layers!

Pour the batter evenly between the prepared cake pans. I like to use a kitchen scale to ensure each pan has exactly the same amount of batter.

Bake for 32-35 minutes, or until a toothpick comes out clean.

Allow the layers to cool in the pans for about 10 minutes, then run an offset spatula around the edge of the pans to help separate the layers from the pans.

Once the layers are fully cooled, carefully flip the pans and remove the layers from the pans.

Use a serrated knife to level the tops of the layers, then set aside.

While the cake layers bake and cool, make the chocolate orange buttercream frosting.

Beat 1 1/2 cups of unsalted butter on a medium speed for 30 seconds with a paddle or whisk attachment until smooth. 

Mix in 1 tsp orange emulsion or extract, 2 Tbsp fresh orange zest and 1/2 tsp salt on a low speed.

Gradually add in 3 cups of powdered sugar on a low speed.

Scrape the sides and bottom of the bowl as needed with a rubber spatula.

Add 1/2 cup of heavy cream half through adding in the powdered sugar to make it easier to mix.

Mix in 1 cup dark cocoa powder on a low speed.

Pour in 2 cups of cooled, melted chocolate.

Beat on low until the ingredients are fully incorporated and the desired consistency is reached.

If the frosting is too thick, add an extra Tbsp of heavy cream. If it's too thin, add in another 1/4 cup of powdered sugar. Repeat until the frosting is the right consistency.

Stir by hand with a rubber spatula to get the frosting SUPER smooth. Cover with plastic wrap and set aside.

If possible, chill your cake layers in the freezer for 20 minutes before assembling the cake. It makes them cold to the touch, which minimizes crumbing and makes them so much easier to frost and stack them.

Spread about 1 Tbsp of orange chocolate frosting onto a greaseproof cake board or plate, then place your first cake layer on top of frosting smear. This helps the layer stay in place as you assemble the cake.

Spread 1/4 cup of orange marmalade directly onto the cake layer, being careful not to pull up too many crumbs.

Spread an even layer of orange chocolate frosting on top of marmalade with a large offset spatula.

Repeat with the remaining cake layers, being sure to flip the top cake layer upside down (cut side down). This makes it easier to get sharp edges on your cake!

Cover the cake in a thin coat of chocolate orange frosting. Smooth using a bench scraper, then chill the cake in the fridge (10 minutes) or freezer (5 minutes) until the frosting is firm to the touch.

Add a second, thicker layer of orange chocolate frosting to the cake, and smooth using a bench scraper or icing comb. I chose to use an icing comb to give the sides of the cake a bit of texture.

Decorate as desired! I chose to add a partial chocolate ganache drip, and used some candied orange slices, orange spirals, and orange zest to decorate the top of the cake.