In a 6-qt. stockpot, cook sausage and onion over medium heat until no longer pink, breaking into crumbles, 6-8 minutes. Remove with a slotted spoon., Add kale to pot; cook and stir 2 minutes. Add garlic and, if desired, pepper flakes; cook 1 minute. Add wine; cook 2 minutes longer., Stir in sausage mixture and remaining ingredients. Bring to a boil. Reduce heat; simmer, covered, until kale is tender, 15-20 minutes.