Chocolate orange blackout cake

Method

1. Heat the oven to 180°C/160°C fan/gas 4. Grease the cake tins with butter and line the bases with baking paper.
2. Put the butter and chocolate in a bowl set over a pan of simmering water (make sure that the bowl isn’t touching the water) and leave to melt, stirring occasionally
3. Meanwhile, sift the flour, baking powder, bicarb, salt, brown sugar and cocoa powder into a large bowl (see tips, below), then stir together to combine.
4. Remove the melted chocolate mixture from the heat, then whisk in the hot coffee and buttermilk, followed by the eggs. Pour the liquid mixture into the dry ingredients, then stir together with a balloon whisk; just enough to form a smooth cake batter. Divide the batter equally between the cake tins, then bake for 35-40 minutes or until the cakes are starting to pull away from the sides of the tin and spring back to a light touch. Remove and set aside to cool for 20 minutes, then turn out onto a wire rack to cool completely.
5. For the ganache (see tips), put the finely chopped chocolate in a large heatproof bowl. Add the cream, golden syrup and a large pinch of salt to a saucepan over a medium heat. Bring the cream mixture to a bare simmer, then pour it over the chocolate. Wait a few minutes, then stir to form a silky smooth ganache. Add the butter and stir slowly until the mixture is smooth. Set aside until the mixture has cooled and thickened to the texture of a soft, spreadable buttercream.
6. Using a serrated knife, trim the domed tops off the cakes so they’re nice and level, then crumble the cut-off tops into a large bowl. Slice each of the cakes horizontally into 2 even layers so you have 4 sponges.
7. For the filling, add the orange zest and sugar to a bowl, then rub together with your fingers until the mixture is fragrant and damp. If you can, leave this to sit for an hour or so and even more of the orange oils will be extracted, resulting in a punchier orange flavour. Add the chilled mascarpone and cream, then the orange juice. Whisk with an electric hand mixer until the cream holds soft peaks that flop over at the tip when the beaters are lifted out.
8. To assemble the cake, put a disc of sponge on a cake stand or serving plate (or a turntable, if you have one, as this will make it easier to decorate). Reserve a little of the cream mixture for the top in a piping bag, then use an ice cream scoop or tablespoon to add a third of the remaining cream on top of the sponge. Smooth it out into an even layer, then put another cake disc on top. Repeat until you have 3 layers of cream, then put the final cake disc on top.
9. Spread the ganache over the top and sides of the cake as evenly as you can,  although don’t worry about how neat it is. Coat the entire cake in the crumbled-up cake scraps, then pipe the reserved cream in 6 neat blobs on top. You can decorate the cake however you like, but I like to sprinkle over some cacao nibs and candied peel, adding a little gold leaf for festive flair.