01 - Heat olive oil in a large soup pot over medium heat. Add the sausage, breaking it apart with a wooden spoon into bite-sized crumbles. Cook until deeply browned on all sides, approximately 5 minutes. Transfer the sausage to a plate using a slotted spoon and set aside.
02 - In the same pot with the rendered drippings, add the diced onion and cook over medium heat, stirring occasionally, until softened and translucent, 3 to 4 minutes. Add the minced garlic and stir continuously for 1 minute until fragrant.
03 - Add the sliced potatoes and chicken broth to the pot. Bring the liquid to a rolling boil over medium-high heat, then reduce to a gentle simmer. Cook uncovered for 12 to 15 minutes, or until the potatoes are fork-tender but not falling apart.
04 - Return the browned sausage to the pot along with the chopped kale. Stir to combine and continue simmering for 5 minutes until the kale has wilted and turned bright green.
05 - Reduce the heat to low and slowly stir in the heavy cream. Season with crushed red pepper flakes, kosher salt, and freshly ground black pepper to taste. Allow the soup to heat through gently, taking care not to bring it back to a boil to prevent the cream from separating.
06 - Ladle the hot soup into warmed bowls. Finish each serving with a generous sprinkle of grated Parmesan cheese if desired, and serve immediately alongside crusty bread.