In a stand mixer, whip the cold whipping cream on medium speed until soft peaks form.
In a separate bowl, mix the cold condensed milk with the cold Guinness stout.
Slowly pour the stout mixture into the whipped cream while mixing on low. Blend for about 2 minutes until fully combined.
Increase the speed to high and beat for another 30β60 seconds to ensure the mixture is smooth.
Add vanilla extract, if using, and gently fold in.
Pour the mixture into a freezer-safe container, cover tightly, and freeze for at least 8 hours or overnight.
Scoop and serve with your favorite toppings.