This jam pairs well with grilled chicken.
4 tbsp. unsalted butter
2 large red onions, sliced thin
¾ cup dry red wine
½ cup sherry vinegar
½ cup white granulated sugar
¼ cup black raspberry liqueur, such as Chambord
Kosher salt and freshly ground black pepper, to taste
Heat butter in a 12″ skillet over medium heat.
Add onions; cook, stirring, until soft
but not browned, about 15 minutes.
Add wine, vinegar, sugar, liqueur, salt, and pepper;
cook, stirring, until thick, 40 minutes; let jam cool.