Preheat the oven to 180°C (350°F/gas mark 4). Grease and line 2 x 20cm (8in) loose-bottomed cake tins with non-stick baking paper.
Using a hand-held electric mixer, cream together the butter and sugar in a large bowl. Add two of the eggs and half of the flour and beat until combined. Add the other two eggs and the rest of the flour along with the orange rind, vanilla, cinnamon, and baking powder and beat vigorously to get a good amount of air into it.
Divide the batter between the prepared tins. Bake in the oven for 25–30 minutes, until the cakes have shrunk slightly from the sides of the tins and spring back when touched in the centre. Remove from the oven and leave the cakes to cool in the tins.
For The Mulled Berries
Put all the ingredients in a heavy-based pan and heat gently until the jam has melted and everything is combined. Add in the frozen berries and gently mix everything. Cook for 5-6 minutes until the berries are coated. Remove from the pot and allow to cool completely prior to using.
Whisk the cream in a bowl until thickened and holding its shape. Put one sponge upside down on a serving plate or cake stand. Using a palette knife, spread on half of the whipped cream. Spoon over three-quarters of the mulled berries, allowing some to drip over the edges, then cover with the second sponge. Pipe or swirl the rest of the whipped cream around the edges on top and spoon the remaining berries into the centre. Decorate with fresh mint, to finish.