The cake part is very easy! Dump the beer, butter, cocoa, flour, sugar, baking soda, salt, eggs and sour cream into a large bowl and mix well!
Once thoroughly mixed, pour the batter into a bundt pan (either sprayed with cooking spray, or greased well with shortening).
Put into a pre-heated oven at 350 degrees for roughly 35-50 minutes (or until cake bounces back to the touch and a test fork or pick comes out clean).
While that cools, you can make the ganache icing. Put the chocolate, cream and coffee in the top of a double-boiler, and melt and stir until smooth. (The coffee is optional, but it adds a lovely flavor which goes quite nicely with the cocoa and stout. Regular or decaf both work fine.) Then drizzle over the cooled cake.
Enjoy! (Pairs fabulously with nice vanilla bean ice cream!)