Split the cake, spoon in the filling and the fresh raspberries, then turn it upside down on to a cake stand. Place the icing sugar into a bowl and gradually add the rosewater, mixing all the time until the icing is thick enough to coat the back of a spoon. Pour over the cake and let it drizzle down the sides. Allow to set for an hour or so.
To make the chocolate curls, place a small heatproof bowl over a saucepan of gently simmering water, making sure the base of the bowl does not touch the water. Add the white chocolate to the bowl and heat until it melts, stirring only very occasionally. Pour it on to a plastic board, or a piece of marble, and spread out with a palette knife. Allow to set; a short spell in the refrigerator will help.
Run a sharp fine knife at a 45-degree angle across the chocolate (or use a vegetable peeler) and it will curl. Too cold and it won’t work; too soft and it will need 15 minutes or so back in the refrigerator. You’ll have to experiment.
Scatter the cake with the chocolate curls, then with the rose petals.