Chocolate Guinness Cake

1.Heat oven to 350 degrees. Butter a 9-inch springform pan and line with parchment paper.
2.In a large saucepan, combine Guinness and butter. Place over medium-low heat until butter melts, then remove from heat. Add cocoa and sugar, and whisk to blend.
3.In a small bowl, combine sour cream, eggs and vanilla; mix well. Add to Guinness mixture.
4.In another small bowl shift together flour and baking soda. Add to saucepan, and whisk again until smooth.
5.Pour into buttered pan, and bake until risen and firm, 55 minutes. Test with toothpick and place pan on a wire rack and cool completely in pan.
5.For the topping, using a hand mixer, beat cream cheese until fluffy. Add powdered sugar and mix until fully incorporated. Add heavy cream, and mix until smooth and spreadable.
6.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.