Preheat your oven to 350°F (175°C) and prepare two 8-inch round cake pans.

In a bowl, whisk together all-purpose flour, granulated sugar, cocoa powder, baking soda, baking powder, and fine sea salt until combined.

In another bowl, mix sour cream, vegetable oil, eggs, vanilla extract, and Guinness until smooth.

Combine wet ingredients into dry ingredients, folding gently until no dry flour remains.

Divide batter into prepared pans and bake for 35-40 minutes.

Remove from oven and cool for 30 minutes before inverting onto a wire rack.

Beat the butter for the frosting until fluffy, then gradually add powdered sugar and Irish cream.

Assemble the cake with one layer on a plate, frosting between layers, and repeat with the second layer.

Apply a thin crumb coat of frosting, chill for 20 minutes, then frost with a thicker layer and decorate.

For ganache, heat cream and pour over chocolate, stir until smooth, then drizzle on the cake.

Slice and serve, pairing with coffee or Irish cream liqueur.