In a large pot, heat a drizzle of olive oil over medium heat. Add the diced onion and sauté until translucent, about 5 minutes.
Add the minced garlic and red pepper flakes, cooking for another minute until fragrant.
Remove the casing from the Italian sausage and add it to the pot. Break it up with a wooden spoon and cook until browned and fully cooked through, about 7-10 minutes.
Stir in the sliced potatoes, then pour in the chicken broth. Bring to a boil, then reduce heat and simmer for about 15-20 minutes or until the potatoes are tender.
Once the potatoes are tender, add the chopped kale and heavy cream to the pot. Stir to combine and cook for an additional 5-7 minutes until the kale is wilted and the soup is heated through.