Prepare candied oranges by combining water and sugar in a saucepan over medium heat. Add the medium orange, simmering for about 30 minutes until tender and syrupy. Remove and let cool.

Preheat your oven to 350°F (175°C) and prepare two 9-inch round baking pans by greasing and lining them with parchment paper for easy release.

Mix the blood orange zest, olive oil, and blood orange juice in a large bowl until well combined.

Combine flour, granulated sugar, cocoa powder, salt, and baking soda in another bowl.

Gradually incorporate the wet ingredients into the dry mixture, stirring gently until just combined.

Stir in an additional 1 1/4 cups of water until fully combined and smooth.

Pour the batter evenly into the prepared pans and bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean. Wait for them to cool completely on a wire rack.

Beat the butter in a mixing bowl until fluffy, then add blood orange zest, powdered sugar, vanilla extract, and blood orange juice. Continue beating until creamy and well blended.

Heat dark chocolate and half and half in a microwave-safe bowl until melted and smooth, stirring every 20 seconds to prevent burning.

Assemble by layering one cake round with buttercream, then topping with the second layer. Finish with a generous drizzle of chocolate ganache over the top and sides.