In a small saucepan, melt butter and whisk together with Guinness, vanilla extract and cocoa. Remove from heat and let cool.
While the Guinness mixture is cooling, grease and line 2 eight inch cake pans with parchment paper.
Next, whisk together the dry ingredients (sugar, flour, baking soda). Pour the cooled Guinness mixture onto the dry ingredients, then whisk in the 2 eggs.
When the batter is shiny and smooth, pour evenly into two prepared cake pans.
Bake for 30-35 minutes, or until a skewer comes out clean.
While the cakes are baking make the buttercream by whipping together the softened butter and sugar in a standing mixer, then adding in just enough Bailey’s to get it loose and fluffy. The key to white frosting is to whip it a long time – the longer you whip it, the whiter it will become. I whipped this for 5-10 minutes.
Once the cakes are done baking, cool completely.
Assemble the cake (leveling the layers with a serrated knife, if needed).
First, add the frosting for the middle layer with about 1/3 of the buttercream.
Top with second layer.
Next we’ll do a crumb coat.
Coat top and sides with another 1/3 of the frosting mixture
Spread it all over, nice and thin. Refrigerate to set it overnight.
Once the crumb coat is firm to the touch, add the final 1/3 of the frosting to the cake – top first, then sides. Spread it around evenly.
Refrigerate cake when through serving.
The only thing I did different was, I using 1/2 Black Cocoa and half the unsweeten cocoa.