Warm a Dutch oven or 6-quart pot over medium-high heat. Once you can feel the heat when you hold your hand 6 inches above the pot, crumble in the Italian sausage.
Cook, stirring occasionally and breaking up the sausage as desired, until the sausage is browned and cooked through, 5-7 minutes. Drain the sausage drippings from the pan.
Return the pot to the heat and add the chicken stock, potatoes, salt and red pepper flakes.
Boil until the potatoes are for-tender, about 15 minutes.
Use a slotted spoon to remove 1 cup of potatoes from the pot and place them in a bowl. Mash the potatoes and pour them back into the pot; this will help thicken the soup.
Add the kale and cream to the soup, and stir to combine. Continue cooking the soup until the kale is wilted and tender, about 3 more minutes.
Taste for seasoning and add salt to taste and red pepper flakes.