Preheat oven to 350° and grease and line with parchment paper a 9-inch pan.
Pour the Guinness into a large saucepan and add the sliced butter. Heat until butter is melted and remove from heat. Whisk in the cocoa and sugar. In a separate bowl, beat the Jameson with the eggs and vanilla. Add the Jameson mixture to the Guinness mixture in the saucepan. Finally, beat in the flour and baking soda.
Pour the batter into the greased and lined pan and bake for 45 minutes to an hour. Cool completely in the pan on a wire rack.
For the frosting, beat the powdered sugar and cream cheese together until well combined and creamy. Add the cream and caramel and beat again until it's a spreadable consistency.
