For the cake

1. Preheat the oven to 180C. Line 2 x 20cm cake tins with baking paper. Mix together the flour and cocoa powder in a bowl. Melt the chocolate, sugar and butter with 100ml water in a pan over low heat until smooth, set aside to cool.

2. Once cooled, transfer to a mixing bowl and whisk in the eggs one at a time until combined, followed by the vanilla extract. Slowly whisk the wet ingredients into the dry ingredients and stir until completely combined. Sprinkle the orange zest in and gently fold.

3. Divide the batter between the cake tins and bake for 30 minutes or until a skewer poked into the middles comes out clean. Leave the cakes for 20 minutes to cool before taking out of the tine and transferring to a wire rack.

For the orange slices

1. Cut the orange into thin slices. Place a medium saucepan over high heat. Add water and sugar, stir to combine and let the sugar dissolve, it should be translucent. Add the orange slices.

2. Bring the mixture to a simmer, then lower the heat. Cover and cook for about 45 minutes on a low heat.

3. Once the time is up, remove the pan from the heat and let the orange slices cool completely while still in the saucepan with the syrup.
   

For the ganache

1. In a small saucepan over medium heat, heat up the cream.

2. Place the dark chocolate and the orange chocolate into a bowl. Once the cream begins to boil, pour it over the chocolate.

3. Stir the mixture until all the chocolate has melted and the cream is completely combined. Cover the ganache and set it aside to cool, so that it sets slightly and becomes a pourable consistency.

For the buttercream

1. Put the chocolate in a heatproof bow, place in the microwave, stirring every 30 secs until the chocolate is completely melted. Leave the melted chocolate to cool for 5 to 10 minutes.

2. Mash the butter and icing sugar together with a fork, then switch to an electric mixer and beat until fluffy.
   

3. Add the cocoa and pour in the melted chocolate, a pinch of salt and the milk, then mix again until smooth but fluffy.
   

To assemble

1. On a cake stand or large plate, sandwich the cakes together with half of the buttercream, then spread the rest on top and around the sides but leave some for extra piping if desired.

2. Pour the chocolate ganache over the cake and use the back of a spoon to gently move some ganache over the edge so that it drips down the side of the cake for decoration.

3. Place in the fridge to set for 15 minutes before piping any extra buttercream around the cake, if desired and propping your orange slices up around the centre of the cake.

   Serve and enjoy!