Step 1: In a large pot or Dutch oven, brown the Italian sausage over medium-high heat until fully cooked. Use a spatula to break the meat into small crumbles.
Step 2: Remove the cooked sausage with a slotted spoon and set aside, leaving about 1-2 tablespoons of fat in the pot. If there isn't enough fat, add a tablespoon of olive oil.
Step 3: Add the diced onion to the pot and sauté for 5 minutes until translucent. Stir in the minced garlic and red pepper flakes, cooking for another 1 minute until fragrant.
Step 4: Pour in the chicken broth and use a wooden spoon to scrape up any browned bits from the bottom of the pot. Add the diced potatoes.
Step 5: Bring the mixture to a boil, then reduce heat to a simmer. Cover and cook for 15-20 minutes, or until the potatoes are tender when pierced with a fork.
Step 6: Optional: Lightly mash a few potatoes with a fork or masher to thicken the broth. Stir the cooked sausage back into the pot.
Step 7: Stir in the heavy cream and the chopped kale. Simmer for another 2-3 minutes until the kale is wilted and the soup is heated through.
Step 8: Season with salt and black pepper to taste. Serve warm with crusty bread.