Spiced chocolate cake with chocolate icing

Ingredients

• a knob of melted butter, for brushing
• 175g soft unsalted butter
• 225g dark chocolate, 50% cocoa solids, chopped
• 150g light muscovado sugar
• 2 tbsp black treacle
• 3 tbsp golden syrup
• 2 balls stem ginger in syrup, drained and finely chopped
• 4 large eggs, lightly beaten
• 125g self-raising flour
• 1 tsp baking powder
• ½ tsp mixed spice
• 1 tsp ground cinnamon
• 1 tsp ground ginger
• 175g dark chocolate, 50% cocoa solids, finely chopped
• 125ml double cream
• 3 tbsp ginger syrup, from the stem ginger jar
• a handful of white chocolate stars, to decorate