This is an easy cake to make and is fantastic as an afternoon pick-me-up. The trick is to make sure you marinate your raisins for 24 hours before baking.
Wash the raisins in warm water (this will open them up a bit and allow the rum to penetrate). Put the raisins and rum in a bowl, cover and leave to soak overnight.
Preheat the oven to 180°C (350°F/Gas 4). Melt the chocolate over a bain-marie (water bat