If the bowl of your ice cream maker has to be frozen, make sure to do so. In a saucepan bring the pint of Guinness to a boil and let it reduce to about half to concentrate the flavor. Whip the egg yolks and sugar until pale and thick. In another saucepan bring the milk and cream to a boil. Pour a bit of the boiling milk mixture over the yolks and whisk continuously to bring everything to the same temperature. Then pour the egg yolk/milk mixture back into the saucepan with the remaining milk and whisk well. Return the saucepan to the stove and cook over medium heat, stirring constantly, until it thickens just enough to coat the back of a wooden spatula. Do not allow the mixture to boil. Strain the mixture through a fine strainer or 2 layers of cheesecloth. Cover loosely and quickly place in an ice bath. Whisk in the Guinness Stout reduction. Place the mixture into an ice cream machine and follow the manufacturer's instructions.