Chocolate Guinness Cake

This recipe was given to us from Laurel Johnson as originally written by Nigella Lawson for Kirsten's cookbook. I made it for Matt's birthday and it was very tasty. I sent one cake to work with Matt and he has received comments such as, "That is hands down, the BEST cake I've ever tasted!" We better hold onto this recipe!  Adapted from: http://www.nigella.com/recipes/view/chocolate-guinness-cake-3086

Ingredients
For the cake:
Butter for pan
1 cup Guinness stout
10 tablespoons (1 stick plus 2 tablespoons) unsalted butter
3/8 cup unsweetened cocoa
2 cups superfine sugar
3/8 cup sour cream
2 large eggs
1 tablespoon vanilla extract
2 cups all-purpose flour
2 1/2 teaspoons baking soda

For the topping:
1 1/4 cups confectioners' sugar
8 ounces cream cheese, at room temperature
1/2 cup heavy cream
A splash (or more) of Bailey's Irish Cream

Heat oven to 350 degrees. Butter a 9-inch springform pan and line with parchment paper. In a large saucepan, combine Guinness and butter. Place over medium-low heat until butter melts, then remove from heat. Add cocoa and superfine sugar, and whisk to blend.
In a small bowl, combine sour cream, eggs and vanilla; mix well. Add to Guinness mixture. Add flour and baking soda, and whisk again until smooth. Pour into buttered pan, and bake until risen and firm, 45 minutes to one hour. Place pan on a wire rack and cool completely in pan.

Using a food processor or by hand, mix confectioners' sugar to break up lumps. Add cream cheese and blend until smooth. Add heavy cream and Bailey's. Mix until smooth and spreadable.
Remove cake from pan and place on a platter or cake stand. Ice top of cake only, so that it resembles a frothy pint of Guinness.