01 - Heat olive oil in a large soup pot over medium heat. Add the Italian sausage, breaking it into small crumbles with a wooden spoon. Cook until evenly browned and no pink remains, approximately 5 minutes. Transfer the sausage to a plate lined with paper towels and set aside, leaving the rendered drippings in the pot.
02 - In the same pot with the reserved drippings, add the diced onion and cook over medium heat until softened and translucent, about 3 to 4 minutes. Add the minced garlic and stir continuously for 1 minute until fragrant, being careful not to let it brown.
03 - Add the sliced potatoes and chicken broth to the pot. Bring the mixture to a rolling boil, then immediately reduce the heat to medium-low. Simmer uncovered for 12 to 15 minutes, or until the potatoes are fork-tender but still hold their shape.
04 - Stir the chopped kale and the previously browned sausage into the soup. Continue simmering for an additional 5 minutes until the kale has wilted and become tender, and the sausage is heated through.
05 - Reduce the heat to low and slowly pour in the heavy cream, stirring gently to combine. Season with crushed red pepper flakes, salt, and black pepper to taste. Allow the soup to heat through for 2 to 3 minutes, but do not bring to a boil to prevent the cream from separating.
06 - Ladle the hot soup into serving bowls. Garnish each portion with freshly grated Parmesan cheese and a crack of black pepper. Serve immediately alongside crusty bread if desired.