Sticky stem gingerbread cake

Name: Sticky stem gingerbread cake
Ingredients: 300g/10oz plain flour; 2 tbsp ground ginger (or according to taste – this makes for quite a hot cake); ½ tsp cayenne pepper (or more if you want it very hot); ½ tsp ground cinnamon; ½ tsp ground allspice; ¼ tsp mace; generous pinch ground cloves; 150g/5½oz butter; 125g/4½ oz dark brown muscovado sugar; 150g/5½oz golden syrup; 50g/1¾ oz syrup from the jar of stem ginger (optional – replace with more golden syrup or honey if not using stem ginger); 200g/7oz black treacle; 250ml/9fl oz milk; 1 heaped tsp bicarbonate of soda; 2 large free-range eggs, lightly beaten; 1 jar stem ginger, drained, washed and very finely chopped (optional)