Bring the beer, cardamom and orange zest to a gentle boil in a saucepan over medium heat; cook, stirring, until reduced to 1 cup, about 10 minutes. Add the butter and brown sugar and cook, stirring only if the mixture looks like it might boil over, until thick and syrupy, 10 to 12 minutes. To test for doneness, drop a bit of caramel into a bowl of cold water. It should form a soft ball; if it doesn't, keep cooking.
Slowly stir in the cream and cook until the sauce thickens, about 5 minutes. Remove from the heat and stir in the vanilla and salt. Remove the cardamom and orange zest with a spoon. Let the caramel cool slightly, then transfer to a small jar. Refrigerate for up to 2 weeks.