Soak the gelatine in a shallow dish of cold water for a few minutes. Meanwhile, put the cream, sugar, milk and rum into a saucepan and slowly bring to a simmer. Heat gently for 30 seconds, then remove the pan from the heat. Taste, adding a little more rum if you wish.
Squeeze the gelatine leaves to remove excess water, then add them to the cream mixture and stir until fully dissolved. Tip the mixture into a jug.
Now pour into four individual glass dishes, leaving enough room for the glaze. Leave to cool, then place the glasses in the fridge to set for at least 2 hours, or overnight if preparing ahead.
To make the pomegranate glaze, heat a dry frying pan. Tip the sugar into the hot pan followed by the pomegranate juice. Bring to the boil and allow to bubble for 10-15 minutes, until thickened to a sticky, syrupy glaze. Pour into a small jug and leave to cool completely.
Pop the chocolate in the freezer for 10-15 minutes before serving. Pour the cooled pomegranate glaze on top of the chilled pannacottas. Take the chocolate from the freezer and draw a small straight-edged knife along the flat side of the bar to make curled shavings. Top each pannacotta with chocolate shavings to serve.