Preheat the oven to 200C/400F. Line 2 x 23cm loose-bottomed non-stick cake tins with parchment paper. Place all of the ingredients for the cake into a bowl and mix together with a hand-held electric whisk (or freestanding electric mixer). Divide the mixture between the prepared tins and bake for 30-35 minutes or until the cakes are spongy when touched and a skewer inserted in to the centre of each cake comes out clean. Leave to cool in the tins for 5 minutes, then transfer to wire racks to cool completely.
Meanwhile, make the frosting. Sieve the orange juice into a small pan and add the rosemary and cook over a gentle heat for about 5 minutes until reduced to about four tablespoons. Remove from the heat and leave to cool, then take out and discard the rosemary. Put into a bowl with the icing butter and vanilla into a bowl and beat together until smooth. Using a hand-held electric mixer, beat in the cream cheese until smooth. Using a palette knife sandwich the cakes together with some of the frosting, then put on a cake stand and spread the remainder all on top. Serve straight to the table, cut into slices on plates to serve. This cake will keep well in a cake tin for up to three