Preheat the oven to 350 degrees.

Prepare two 9” round cake pans by greasing and then dusting with either flour or cocoa powder. Shake out the excess. Set aside.

Sift the flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large mixing bowl.

Stir in the orange zest.

Whisk the orange juice, buttermilk, oil, eggs, and vanilla together in a large bowl until well mixed.

Slowly mix the wet ingredients into the dry ingredients, whisking until just incorporated.

Fold in the chocolate chip if using.

Evenly divide the batter between the two prepared cake pans. Give them a soft tap on the counter to shake out any air bubbles.

Bake for 30-35 minutes or until the toothpick test returns clean. You can also gently press the center of the cake with your finger. If it springs back, the cakes are done.

Remove and allow the cakes to cool in the pans for at least 20 minutes at room temperature.

Remove from the pans and cool completely on a wire rack before decorating.

Beat the softened butter in a mixing bowl with the paddle attachment until it is creamy.

Slowly sift the cocoa powder and salt into the butter as it is mixing.

Gradually mix in the confectioner’s sugar, working one cup at a time and mixing well after each addition. You can adjust the sweetness during this time, adding more or less sugar.

Once combined, stir in the orange zest and orange juice. If the frosting is too thick, you can add more orange juice until it reaches your desired consistency. (more sugar will thicken the frosting)

Increase the speed and beat the frosting for several minutes to give it a good whip and make it lighter in consistency. You can add the vanilla during this time while it is whipping at high speed.

Place one layer of cake on the cake plate. Top it with a dollop of the frosting and spread into an even layer.

Add the second cake layer on top of the frosting/filling. Add more frosting on top and smooth it out. Add more to smooth out over the sides of the cake. Continue adding more frosting to the sides and the top, smoothing into an even layer until all of the cake is coated in the frosting.

Garnish with chocolate ganache, fresh orange slices, candied oranges, orange zest, or chocolate curls or shavings.