For The Frosting, Place The Cream In A Medium-Size Heavy Saucepan Over Medium Heat.
Bring To A Simmer, And Then Remove From The Heat.
Stir In The Chopped Chocolate, And Stir Until All The Chocolate Has Melted And The Mixture Is Smooth.
Pour The Icing Into A Stainless Steel Bowl, And Set Aside On The Counter Until Ready To Frost The Cake.
You Can Make This Up To 3 Hours In Advance.
For The Cake, Place A Rack In The Center Of The Oven, And Preheat The Oven To 350°F.
Grease And Flour Three 8″ Round Cake Pans That Are At Least 2″ Deep, And Shake Out The Excess Flour.
Set The Pans Aside.
Place The Stout And Butter In A Large Saucepan, And Stir Over Medium Heat Until The Butter Melts, 3 To 4 Minutes.
Whisk In The Cocoa Until Smooth.
Remove The Pan From The Heat And Let It Cool.
Place The Flour, Sugar, Baking Soda, And Salt In A Large Bowl, And Whisk To Combine.
Set Aside.
Place The Eggs And Sour Cream In A Large Bowl, And Blend With An Electric Mixer On Medium Speed Until Just Combined, 1 Minute.
Add The Chocolate And Butter Mixture And Blend Just To Combine.
Fold In The Flour Mixture, And Scrape Down The Sides Of The Bowl With A Rubber Spatula.
Divide The Batter Between The Prepared Pans, And Place The Pans In The Oven.
Bake The Cake Until The Top Springs Back When Lightly Pressed With A Finger, 30 To 35 Minutes.
Remove The Cake From The Oven, And Place The Pans On A Wire Rack To Cool For 10 Minutes.
Run A Knife Around The Edges Of The Pans, Give The Pans A Gentle Shake, And Invert The Layers Once And Then Again So The Layers Cool Completely Right Side Up, About 1 Hour.
To Assemble The Cake, Stir The Frosting Until Smooth Enough To Spread.
Place 1 Layer On A Cake Plate, And Spread With About ⅔ Cup Of Frosting.
Top With The Second Layer, And Spread With Another ⅔ Cup Of Frosting.
Top With The Third Layer And Spread The Top And Sides Of The Cake With The Remaining Frosting.
Slice And Serve.
