In a large saucepan, cook the sausage and onion over medium heat for 4 to 6 minutes or until the sausage is no longer pink and the onion is tender, breaking up the sausage into crumbles; drain.
Stir in the seasonings. Add the potatoes, kale, milk and cream; bring to a boil. Reduce the heat; simmer, covered, for 10 to 15 minutes or until the potatoes are tender.
In a small bowl, mix the cornstarch and water until smooth; stir into the soup. Return to a boil, stirring constantly; cook and stir for 1 to 2 minutes or until thickened.