In a medium bowl, combine flour, baking soda and salt; set aside.
In a large microwaveable bowl, melt 6 ounces of chocolate and butter on 50% power for one minute. Stir and continue to melt at 50% power until smooth. (Mixture can also be melted on top of the stove in a heavy saucepan over low heat). Transfer mixture to a large bowl. Add sugar and beat with an electric mixer until well blended. Add eggs and vanilla; beat until combined. Add flour mixture and Guinness® Stout, alternating between the two; beat until just combined. Divide evenly between two prepared pans, filling pans about 2/3rds full.
Bake 38-40 minutes or until toothpick inserted into the center comes out clean. Cool 10 minutes in pans; remove and cool completely on cooling grid.
For icing, combine Harp® lager and salt in a large skillet. Heat over medium-high heat until liquid has reduced to about 1/3 of a cup; about 30-35 minutes. Remove from heat and cool completely.
In a large bowl, beat butter and shortening with electric mixer until fluffy. Gradually add confectioners? sugar, one cup at a time, beating on low speed. Add reduced lager, one tablespoon at a time, continuing to beat on medium speed until light and fluffy. If icing is too soft add additional confectioners? sugar, one tablespoon at a time, until desired consistency is reached.
To assemble, spread icing onto one layer of cake; top with second cake layer. Using a spatula or spoon, ice top and sides of cake with remaining icing. Shave remaining 2 ounces chocolate with peeler; press onto sides of cake.