Recipe based on Nigella Lawson from the Cooking Section of the New York Times.
Preheat cooker (oven) to 350 degrees (F). Butter a 9-inch springform pan and line with parchment paper.
In a large saucepan, combine Guinness and butter. Place over medium-low heat. Add cocoa and superfine sugar, then whisk. Cook just until butter melts and sugar dissolves. Remove from heat and cool to room temperature.
In a small bowl, combine: sour cream, eggs, and vanilla. Mix well. Add to the Guinness mixture. Now add the flour and baking soda. Whisk until smooth.
Into the buttered pan she goes, and bake until risen and firm, 45 minutes to one hour. Place pan on a wire rack and cool completely in pan.
In a food processor or by hand, combine confectioners' sugar (break up lumps) and cream cheese and blend until smooth. Add heavy cream, mix until spreadable.
Remove cake from pan. Place on a platter or cake stand. Ice top of cake, make it look like a nice pint of Guinness with a frothy head.
Add some Baileys Irish Cream in the frosting -- to taste.
If using unsalted butter, add 1/2 teaspoon salt to the recipe with the flour.
*I found the frosting too thin as written (using 1/2 cup heavy cream). I added 2 cups extra confectioners' sugar or use only a few tablespoons of heavy cream to obtain the desired consistency.
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