In a saucepan, simmer the Guinness until it reduced by 3/4. This means you need to cook it down to about 3 oz. It took me about 15 minutes, but it might take you less than that. Pour it into a measuring cup and set it aside.

In a saucepan, combine the cream, half-and-half, sugar, and vanilla. Bring it to a gentle boil over medium heat, then remove from the heat.

In a bowl, beat the 6 egg yolks. Slowly whisk in 1 cup of the hot cream mixture.

Then whisk that mixture into the rest of the cream. Cook the mixture some more until it reaches 170 degrees. I used a candy thermometer.

Combine it with the Guinness reduction, and pour it into a pitcher (or bowl). Place a piece of plastic wrap over it, touching the surface so it does not form a pudding skin. and chill it at least 2 hours or overnight.

When you are ready to process it into ice cream, strain the mixture. (I use a jelly bag).

Process it in your home ice-cream maker according to those directions.