Heat the olive oil in a medium saucepan over medium heat add onion, salt, and a few turns of black pepper. Saute until the onion is caramelized about 15 minutes. Add cranberries, brown sugar, balsamic vinegar, and orange juice. Bring to a boil then reduce to a simmer. Cook until the sauce is jam-like in consistency, about 40 minutes stirring occasionally. Cool transfer to a container cover and refrigerate up to one week.