01 - Heat olive oil in a large soup pot over medium heat. Add the sausage with casings removed and cook, breaking it into small crumbles with a wooden spoon, until evenly browned throughout, approximately 5 minutes. Transfer the browned sausage to a plate and set aside, leaving any rendered drippings in the pot.
02 - In the same pot with the residual drippings, add the diced onion and cook over medium heat until softened and translucent, 3 to 4 minutes. Add the minced garlic and stir continuously for 1 minute until fragrant, taking care not to let it brown.
03 - Add the thinly sliced potatoes and chicken broth to the pot. Bring the liquid 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 holding their shape.
04 - Return the browned sausage to the pot along with the chopped kale. Stir to combine and continue simmering for an additional 5 minutes until the kale has wilted completely and the flavors have melded.
05 - Reduce the heat to low. Pour in the heavy cream and stir gently to incorporate. Season with crushed red pepper flakes, salt, and black pepper to your preference. Allow the soup to heat through gently for 2 to 3 minutes, but do not bring to a boil after adding the cream.
06 - Ladle the hot soup into warmed bowls. Finish each portion with a generous sprinkle of grated Parmesan cheese if desired. Serve immediately alongside crusty bread for dipping.