Preheat your oven to 350°F (175°C) and prepare your cake pans.
In a large bowl, combine the stout and cocoa powder until smooth.
In a separate bowl, whisk together the flour, sugar, baking soda, and salt.
Combine the dry ingredients with the stout mixture, stirring until just combined.
Incorporate the vegetable oil, vanilla extract, and eggs into the batter.
Divide the batter evenly between the prepared cake pans and smooth the tops.
Bake in the preheated oven for 30-35 minutes until a toothpick comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.
While the cakes cool, prepare the cream cheese frosting by beating together the cream cheese, powdered sugar, and milk until smooth.
Once the cakes are completely cool, frost the top of one layer, then place the second layer on top and frost the top and sides of the cake.
Decorate with optional cocoa powder or chocolate shavings before serving.