Heat oven to 180C/160C fan/gas 4. Rub a little butter over the base and sides of two 20cm cake tins (use cake tins rather than sandwich tins as the higher sides work better), then line the base and sides with baking parchment. Melt 150g butter with 100g of the chocolate in a bowl set over a small saucepan of gently simmering water – make sure the base of the bowl doesn’t touch the water. Stir the butter and chocolate every min or so until it has melted. Set aside to cool a little.
Meanwhile, measure 250g flour, 2 tsp baking powder, ½ tsp bicarb and 250g sugar in a large bowl. Make a well in the middle and add 150g yogurt, 2 tsp vanilla extract, the orange zest and juice, 3 eggs and 2 tbsp milk. Whisk everything together, then stir in the melted butter and chocolate.
When the cake mixture is smooth (this makes a very wet pourable batter), divide it equally between the two cake tins. Bake on the middle shelf for 25-30 mins, they will look golden and evenly risen when cooked. Check they are done by pushing a skewer into the centre of the cakes – it should come out clean. If there is any wet cake mixture on the skewer, return the cake to the oven for a few more mins, then check again.
Leave the cakes to cool in their tins for 5 mins, then transfer to a cooling rack. Wash out the tins and repeat steps 1 and 2, to make two more sponges in total. You can make them a day or two before icing, then wrap them in a double layer of cling film once cool. They can also be frozen for up to two months.
To make the compote, simmer the cranberries and sugar in a small pan for 4-5 mins until jammy, then leave to cool.
For the icing, melt the chocolate, either in 20-30 secs bursts in a microwave or in a bowl over simmering water. Set aside to cool a little. Roughly mash the butter and icing sugar together, then beat until smooth with an electric whisk or mixer. Add the chocolate and cream cheese and beat again until smooth.
To assemble the cake, place one sponge on a cake board the same size as the sponge, then sandwich the other sponges on top with a little icing and the cranberry compote. Use the cake with the neatest edge, flipped upside down, on top to give your cake a good shape.
Pile about half the remaining icing on top of the cake and use a palette knife to spread it thinly over the top and down the sides of the cake. This is a crumb coat, it catches any crumbs, ensuring the final layer looks clean and professional. Chill the cake for 10-20 mins to firm up the icing or leave it somewhere cool for longer. Will keep for three days.
To decorate the cake: dot the top with meringue kisses that you've either bought or made yourself, edible snowflake decorations and gold leaf, if you like.