This isn't my recipe at all, I found it (via a friend) on the Sprinklebakes blog, and she herself got it from Epicurious.
However, I've made it a few times now and everyone loves it, so reposting here with my notes and modifications to share the joy (and also so I can easily find it again).
4 egg yolks
0.5 cups sugar, plus 3 tablespoons
1.5 cups of Guinness stout beer
2.25 cups of heavy whipping cream
4 ounces of dark chocolate (I used 72%). Chop or break it up into smaller pieces so it melts faster.
Pour 1 cup of Guinness into a small saucepan and set it on the stove to simmer over medium heat.
In a separate bowl, mix egg yolks and 0.5 cups of sugar.
Pour the remaining 0.5 cups of Guinness into another saucepan (pour slowly down side to minimize foaming) and add 1.25 cups of the heavy cream. Mix, and set on stove over medium heat. Stir occasionally until bubbles start to form at edges. At this point, remove saucepan from heat. And add the 4 oz. chocolate, and stir until chocolate is all melted and mixture is smooth. (NOTE: this step is important. If the cream gets too hot, the chocolate will go grainy and the pudding not have a smooth texture. If you do overheat the saucepan to boiling point, let it cool down for a bit before adding the chocolate.)
Add the sugar and egg yolk mixture to the chocolate mixture in the saucepan, stirring constantly while adding. Return the saucepan to the heat. Stir constantly for about 5-10 minutes - the original recipe says "till it thickens" but it's very hard to tell the difference. When thickened the mixture should coat the back of a spoon dipped into it, and not be runny.
At this point, remove from heat again and divide among small glasses. Leave at least an inch of space in each to add the topping. This is a VERY rich pudding, so keep the glasses quite small - this amount should make about 6 glasses. Refrigerate for at least an hour, until set (cover with plastic wrap if leaving overnight).
Meanwhile ... the first saucepan should have simmered down to just a tablespoon or two of liquid. (If not, keep simmering till it does.) This is making a Guinness flavoured reduction, so you really only want a small amount of concentrated liquid left. Pour the reduction into a bowl and put in the fridge to cool.
(Wait at least an hour to do the next step, or overnight, so that the Guinness reduction and the pudding have time to cool.)
In a clean bowl, beat the remaining 1 cup of heavy cream with the remaining 3 tbs of sugar. Beat until soft peaks form, then add the cooled Guinness reduction and beat again until all combined. Carefully spoon the whipped cream topping onto the top of the pudding glasses and return to fridge to cool until ready to serve.
(Ideally, I guess you'd find some teeny glasses that look like miniature beer steins ... but this was what I had at the time.)
Mmmm, tasty. I'm not at all a pudding fan, and not a huge Guinness fan either, but this is definitely delicious!