Preheat your oven to 180°C (350°F) and grease a 9-inch springform pan with butter, lining the bottom with parchment paper.

Melt 250g of unsalted butter in a medium saucepan over low heat, whisk in 250ml of Guinness beer, followed by 75g of cocoa powder and 300g of caster sugar until smooth.

In a large bowl, whisk together 200g of sour cream, 2 large eggs, and 1 teaspoon of vanilla extract until frothy, then pour into the warm butter-Guinness mixture.

Sift 250g of plain flour and 1 teaspoon of bicarbonate of soda in a separate bowl, then gradually add this to the wet ingredients, mixing gently until just combined.

Pour the batter into the prepared pan and bake for approximately 60 minutes, checking doneness with a toothpick.

Remove from the oven and let cool in the pan for about 15 minutes before transferring to a wire rack.

To prepare the icing, beat together 200g of cream cheese and 100g of softened butter until smooth, then gradually add the icing sugar and Baileys to taste.

Spread the Baileys icing generously over the cooled cake and decorate as desired.