Preheat your oven to 170C/150 Fan, and line two 8"/20cm cake tins with baking parchment.
In a stand mixer, or a large bowl, beat together the unsalted butter and light brown soft sugar until light and fluffy.
Add in the eggs, self raising flour, cocoa powder and orange extract and beat again until combined well.
Split the mixture between the two tins.
Bake the cakes in the oven for 50-60 minutes, or until baked through - check with a skewer to make sure they're done!
Leave the cakes to cool in the tins for 10 minutes, and then take out and leave to cool fully on a wire rack!
Buttercream
Beat the unsalted butter on its own for minute or two, to soften it and loosen it.
Add in the icing sugar and beat well until smooth and fluffy.
Finally, add in the melted terry's chocolate orange and beat again until smooth.
Decoration
Split the two cakes into four layers in total.
Put the first cake onto a cake board of plate. Add a little buttercream and spread. Repeat with the second and third sponges. Add the final sponge on top.
Using a small amount of buttercream, spread and smooth around the cake sides and top for a crumb coat and add to the fridge for at least 30 minutes.
Once set, add more buttercream onto the tops and sides of the cake, and smooth around covering the cake completely in buttercream.
Once finished, put the cake in the fridge again for at least 30 minutes.
Ganache
Add the dark chocolate, milk chocolate and double cream to a bowl, and microwave until smooth.
Using a small piping bag or a teaspoon, drip the ganache down the sides of the cake.
Set the cake in the fridge again for 30 minutes!
Finish the cake off by piping on any leftover buttercream, and adding any sprinkles and terry's chocolate orange segments!