Heat a large stock pot or Dutch oven over medium-high heat. Add the Italian sausage, chopped onion, and garlic. Cook until the sausage is browned and cooked through, breaking it into small pieces as it cooks.
Add the chopped potatoes, chicken broth, water, cooked bacon, red pepper flakes, salt, and black pepper. Stir everything together.
Simmer the potatoes. Bring the soup to a boil, then reduce the heat to low. Cover and simmer for 15-20 minutes, or until the potatoes are fork tender.
Add the kale and sausage. If you removed the sausage mixture from the pot, return it to the soup. Add the chopped kale and stir.
Add the cream. Bring the soup back to a gentle boil, then stir in the heavy cream. Once the soup is hot and the kale is tender, remove it from the heat.
Serve. Ladle the soup into bowls and serve immediately with warm breadsticks, crusty bread, or freshly grated Parmesan cheese.
How to Make Zuppa Toscana in the Slow Cooker
Brown the Italian sausage with the chopped onion and garlic in a large skillet over medium-high heat. Break the sausage into small pieces as it cooks.
Transfer the cooked sausage mixture to a slow cooker. Add the chopped potatoes, chicken broth, water, bacon, red pepper flakes, salt, and black pepper. Stir to combine.
Cover and cook on HIGH for about 4 hours or LOW for about 6 hours, or until the potatoes are tender.
Stir in the chopped kale and heavy cream. Cover and cook on HIGH for another 30-45 minutes, until the kale is tender and the soup is heated through.
Ladle the soup into bowls and serve warm with homemade breadsticks or crusty bread.