Pour room temperature stout beer into a small heavy bottom sauce pot. Set over medium heat and bring to a simmer. Heat until beer has reduced to ¾ cup (6 oz). Remove from heat and set aside.
In a medium sauce pot, combine cream, milk, and one tablespoon of sugar. Set over medium heat and bring to a simmer. Stir as necessary to ensure milk does not burn along the sides or bottom of pot.
Meanwhile, in a large bowl, whisk together egg yolks and remaining sugar. Once milk mixture has almost come to a boil, lower heat. Temper hot milk into sugar-yolk mixture. Slowly add hot milk into sugar-yolk mixture about ¼ cup at a time, whisking to distribute heat. Once all the milk has been added to yolk mixture, transfer all contents back into the sauce pot.
Pour in concentrated stout. Stir over medium-low heat until mixture reaches nappe consistency, or 180°F on a kitchen thermometer. Stir frequently to ensure mixture does not burn along the bottom of pot. Let mixture sit at 180°F for 2 minutes to pasteurize eggs. Remove from heat and stir in salt.
Transfer mixture to an airtight container and let mature in the fridge overnight. Freeze mixture in your ice cream maker according to your unit's instructions.
Continue to churn until the volume has increased by half and has thickened to a soft serve consistency. Transfer ice cream to a freezer safe container and freeze for at least 30 minutes. Allow ice cream to sit at room temperature for 5 minutes to soften before scooping and serving.