In a large pot over medium-high heat, cook Italian sausage, breaking it into crumbles with a wooden spoon, until browned and crispy in spots, about 8-10 minutes. Remove sausage to a plate, leaving 1 tablespoon of drippings in the pot.
Add chopped bacon to the pot and cook until crispy. Add diced onion and cook until softened, about 5 minutes. Add garlic and red pepper flakes, cooking for 1 minute until fragrant.
Pour in chicken broth and water, then add sliced potatoes. Bring to a boil, then reduce heat and simmer until potatoes are tender, about 12-15 minutes.
Return cooked sausage to the pot. Stir in chopped kale and cook for 3-4 minutes until wilted and tender.
Reduce heat to low and stir in heavy cream. Season with salt and black pepper to taste. Let soup rest for 5-10 minutes before serving to allow flavors to meld and broth to thicken slightly.