01 - Heat olive oil in a large soup pot over medium heat. Add the sausage, breaking it into crumbles with a wooden spoon, and cook until evenly browned throughout, approximately 5 minutes. Transfer the sausage to a plate and set aside.
02 - In the same pot, cook the diced onion over medium heat until translucent, about 3 to 4 minutes. Add the minced garlic and stir for 1 minute until fragrant.
03 - Add the sliced potatoes and chicken broth to the pot. Bring to a boil, then reduce the heat and simmer uncovered for 12 to 15 minutes until the potatoes are just tender when pierced with a fork.
04 - Return the browned sausage to the pot and add the chopped kale. Simmer for an additional 5 minutes until the kale has wilted and is tender.
05 - Reduce the heat to low. Stir in the heavy cream and season with red pepper flakes, salt, and black pepper to taste. Heat through gently but do not allow the soup to boil after adding the cream.
06 - Ladle the soup into bowls and garnish with grated Parmesan cheese if desired. Serve immediately.