If you want to make candied orange slices, we would suggest making them ahead of time. They're pretty simple, but if you're looking for specifics, this recipe is a good one! Preheat your oven to 325 F (160 C). Butter a loaf pan or line with parchment paper.
Add your room temperature butter and sugar to a stand mixer with the paddle attachment and beat together until very light and fluffy, about 5 minutes. Make sure to scrape down the sides every once in a while.
Add in your room temperature eggs one at a time. Mix well after adding each egg! It's important that they are room temperature or your batter may split and look lumpy. If you find that it still splits, keep mixing for a bit longer. Don't worry too much if it stays lumpy, as adding dry ingredients later will help bind the batter together.
Once your eggs have been incorporated, add the vanilla extract and orange zest and mix. In a separate bowl, combine the dry ingredients - cocoa powder, flour, baking powder, and salt.
Sift in half of the dry ingredients and mix together until just incorporated. Then add half of your room temperature sour cream and mix until incorporated. Sift in the remaining dry ingredients, mix, then add the remaining sour cream. Once incorporated, give the mixture a few folds with a spatula to make sure everything from the bottom has been mixed. (Note: Your batter shouldn't look split/curdled at this stage. If it does, it may affect the texture of the final cake. Of course, you can still bake it and see what happens!)
Add your batter to the loaf pan. Don't worry if it doesn't seem like enough - it will rise!
Bake for 45-55 mins or until a cake tester comes out clean. Check it at 45 - you don't want to overbake it! Let cool completely before cutting into the cake.
For the decoration: Make chocolate ganache by heating your cream until just below boiling. Pour the cream over your chopped chocolate and stir gently until the chocolate has melted. Leave to cool at room temperature or put it in the fridge to set up faster! If you find that it is too solid from the fridge, put it in the microwave for just a few seconds at a time until you can stir it again.
Once your cake has fully cooled, top with ganache and candied orange slices! Enjoy!