Preheat the oven to 180°C/350°F/Gas mark 4. Grease a 23cm/9in round cake tin.
Mix together the sugar, molasses and boiling water. While the mixture is still hot, stir in the butter and the bicarbonate of soda. Leave to cool. Add the raisins, nuts and egg.
Sift together the flour and spices, and stir into the molasses mixture. Pour the mixture into the cake tin and bake for 35–40 minutes until an inserted skewer comes out clean. Turn out onto a wire rack to cool.