Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large saucepan, combine the Guinness and butter over medium heat. Stir until melted and combined.

Remove from heat and whisk in the cocoa powder, flour, sugar, baking soda, and salt until well combined.

In a separate bowl, whisk together the buttermilk, eggs, and vanilla extract. Add to the Guinness mixture and mix until smooth.

Divide the batter evenly between the prepared cake pans.

Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.

Let the cakes cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.

In a mixing bowl, beat together the softened cream cheese and butter until smooth and creamy.

Gradually add the powdered sugar, mixing until fully incorporated.

Mix in the Guinness until the frosting is smooth and spreadable.

Once the cakes are completely cool, place one layer on a serving plate.

Spread a generous amount of frosting on top of the first layer.

Place the second layer on top and frost the top and sides of the cake.

Optional: Decorate with chocolate shavings or additional frosting decorations.