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 browned throughout, about 5 minutes. Transfer the sausage to a plate and set aside, leaving any rendered fat in the pot.
02 - In the same pot, add the diced onion and cook until softened and translucent, 3 to 4 minutes. Stir in the minced garlic and continue cooking for 1 minute until fragrant.
03 - Add the sliced potatoes and chicken broth to the pot. Bring to a boil, then reduce the heat to medium-low and simmer uncovered for 12 to 15 minutes, until the potatoes are fork-tender.
04 - Stir the chopped kale and the reserved cooked sausage back into the pot. Simmer for an additional 5 minutes until the kale has wilted and the flavors meld together.
05 - Reduce the heat to low. Pour in the heavy cream and stir gently to combine. Season with red pepper flakes, salt, and black pepper to taste. Heat through gently, but do not bring to a boil.
06 - Ladle the soup into warm bowls and garnish with grated Parmesan cheese if desired. Serve immediately with crusty bread alongside.