01 - Heat olive oil in a large soup pot over medium heat. Add the sausage, breaking it into small crumbles with a wooden spoon. Cook until deeply browned on all sides, about 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, stirring occasionally, until soft and translucent, 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 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 still hold 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 and turned bright green, and the sausage is heated through.
05 - Reduce the heat to low and slowly pour in the heavy cream, stirring gently to incorporate. Season with crushed red pepper flakes, kosher salt, and freshly ground black pepper to taste. Allow the soup to warm through for 2 to 3 minutes, making sure it never reaches a boil to prevent the cream from separating.
06 - Ladle the hot soup into warmed bowls and finish with a generous sprinkle of grated Parmesan cheese. Serve immediately with crusty bread alongside.