Chocolate and burnt butterscotch layer cake

Name: Chocolate and burnt butterscotch layer cake
Cook time: 2 h 15 min
Total time: 2 h 15 min
Cuisine: British, European
Ingredients: 200g dark chocolate; 200g butter, cut into small pieces; 1 tbsp mixed with 120ml water instant coffee; 3 medium eggs; 2 tbsp buttermilk; 100g self-raising flour; 100g plain flour; ¼ tsp bicarbonate of soda; 300g golden caster sugar; 25g cocoa powder; 200g golden caster sugar; 100g soft light brown sugar; 90g butter; 400ml double cream; 250ml mascarpone; 1 tsp vanilla extract; 1 tbsp Kahlúa or other coffee liqueur