In a large pot, heat the olive oil over medium heat. Add the Italian sausage and cook, breaking it up into crumbles, until browned, about 5-6 minutes. Drain any excess fat if needed.
Add the diced onion and garlic to the pot and sauté for 4-5 minutes until softened and fragrant.
Pour in the chicken broth, and add the sliced or cubed potatoes, Italian seasoning, and red pepper flakes (if using). Stir to combine and bring the soup to a boil.
Reduce the heat to a simmer, cover, and cook for 15-20 minutes, or until the potatoes are tender.
Stir in the heavy cream and chopped kale, cooking for an additional 5 minutes until the kale is wilted and the soup is heated through.
Season with salt and pepper to taste. Serve hot, garnished with grated Parmesan cheese if desired.