1. Preheat the oven to 350°F (180°C). Grease a 9×5 inches (23x12cm) loaf pan and line with a strip of baking parchment. Add the butter and sugar to a large bowl and mix until light and fluffy. Add the egg and mix until well combined. Mix the flour with cocoa powder, baking soda, and salt in a separate bowl. Add alternating with the beer in two batches to the bowl and mix until just combined – do not overmix. Add the chopped chocolate and chopped walnuts and fold in. Pour into the prepared pan and bake for 50-60 minutes or until a wooden skewer inserted into the center of the cake comes out clean. Take the cake out of the oven and let cool down in the pan for 10-15 minutes, then remove from the pan and let cool down completely on a wire rack.

 

2. For the topping chop the chocolate and add together with the sour cream and sugar to a microwave-safe bowl and heat up gently until the chocolate has melted. Stir to combine. Add the hot water and mix in. Decorate the cake with the cream. Let cool/dry before slicing.