Heat oven to 160C/140C fan/gas 3. Grease 2 x 16cm hemisphere cake tins, then dust with flour and shake out the excess. Stand the tins on two ramekins placed on a baking tray to hold them steady. Put the cake ingredients in a large mixing bowl, add a pinch of salt and whisk together until smooth and evenly coloured bright red. Divide the mixture between the two tins and bake for 45 mins. Remove from the oven, cool in the tins for 10 mins, then tip onto a wire rack and leave until completely cold.
Meanwhile, make the chocolate-orange ganache and the filling. Pour the cream into a saucepan, add the orange zest and heat until just steaming. Put half the white chocolate in a bowl, and the dark and
milk chocolates in another bowl. Pour 50ml of the hot cream over the white chocolate (strain it if the orange zest is in big strands), and the remaining cream over the dark and milk mixture. Leave the bowls for 1-2 mins, then stir until smooth and glossy. Set aside to cool for 10 mins.
Put the cream cheese in a bowl and whisk lightly to loosen. Add the icing sugar and the cooled white chocolate and cream mixture, then blend until smooth. Stir through the cranberries, then chill.
When the cakes are cold, you can start assembling. With the cakes flat-side up, use a 7cm biscuit cutter to mark a circle in the centre of each. Use a spoon to gently scoop a dip in each cake, about 4cm deep (save the crumbs for cake truffles – see tip, left.) Remove the cream cheese mixture from the fridge and use to fill the cavities in the cakes, spreading a little onto the flat surfaces too, to help them stick together. Invert 1 cake onto the other to create a sphere, and place on a wire rack set over a baking tray (this will catch any chocolate drips).
To ice the cake, the chocolate ganache needs to be the right consistency – pourable but not too runny. If it has set a little too much, place in the microwave for 10-20 secs, then mix until smooth; if it is too runny, chill until it has firmed up a little. Pour half the ganache over the cake, letting it cover the sides and run into the tray below (use the chocolate drips for cake truffles, see Tip). Cover the whole surface using a palette knife. This is just the first coating, so won’t fill the gap between the sponges. Chill the cake for 20 mins or until the ganache has firmed up a little.
Remove the cake from the fridge. Cover the gap around the middle with the remaining ganache, smoothing it all over with a palette knife. Return to the fridge for another 20 mins until firm, then transfer to a serving plate.
Melt the remaining white chocolate in the microwave in short 10-sec bursts. Drizzle over the top of the cake, then scatter with dried cranberries, sprinkles and edible glitter, if you like. Chill if not serving straight away – it will keep in the fridge for up to 2 days. Remove from the fridge 30 mins before serving.