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

In a saucepan, combine the Guinness and butter over medium heat until melted. Remove from heat and whisk in cocoa powder until smooth.

In a large bowl, mix together sugar, flour, baking soda, and salt.

Add the Guinness mixture, eggs, and sour cream to the dry ingredients and mix until just combined.

Divide the batter evenly between the prepared cake pans and smooth the tops.

Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes before transferring to a wire rack.

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

Gradually add the powdered sugar and mix until well combined.

Add the Guinness and mix until smooth and fluffy.

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

Spread a layer of frosting on top of the first cake layer.

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

Decorate as desired, then slice and serve.