Preheat oven to 180 degrees C. Grease a 20x26cm cake tin and line with baking paper.
Combine prunes and water in a saucepan and bring to the boil then simmer 10 minutes or until prunes are very soft. Add bicarb soda and stir then remove from heat.
Beat the butter and caster sugar in an electric mixer until pale and thick. Add the eggs, one at a time, beating well after each addition. Sift the combined flour, cocoa and spices and stir into the butter mixture. Add the vanilla and prunes.
Pour the mixture into the cake tin and bake 30-40 minutes or until it tests cooked. Serve with ice cream and caramel sauce.