In a large Dutch oven or soup pot over medium-high heat, brown the Italian sausage while breaking it into small crumbles until cooked through.
Remove the sausage with a slotted spoon and set aside, leaving approximately 1 tablespoon of rendered fat in the pot.
Add the diced onion to the pot and sauté for 5 minutes until translucent.
Add the minced garlic and cook for 1 minute until fragrant.
Pour in the chicken broth and add the cubed potatoes, salt, pepper, and red pepper flakes.
Bring the liquid to a boil, then reduce heat to low and simmer for 15 minutes or until the potatoes are fork-tender.
Return the cooked sausage to the pot and stir in the chopped kale.
Stir in the heavy cream and simmer for 3 minutes until the kale has wilted.
Remove the pot from the heat and stir in the grated Parmesan cheese until fully melted and incorporated.
Adjust seasoning with salt and pepper to taste before serving.