Lightly muddle the cardamom pods and cinnamon stick in a small saucepan to release their aromas.

Pour the Guinness into the saucepan.

Bring the mixture to a boil over medium heat.

Reduce the heat to low and simmer gently for 1 minute to allow the flavors to meld.

Remove the saucepan from the heat and let the spiced Guinness cool slightly.

Strain the cooled Guinness through a fine-mesh sieve into a jar to remove the spices.

Cover the jar tightly and refrigerate for up to 3 weeks to allow the flavors to fully develop.