Sauté the Sausage: Set your Instant Pot to the sauté mode. Once hot, add the Italian sausage and cook, breaking it apart with a spoon, until it’s browned and cooked through (about 5-7 minutes). Remove the sausage and set it aside. Leave the rendered fat in the pot.
Sauté the Vegetables: In the same pot, add the chopped onion and garlic. Sauté for 2-3 minutes, until fragrant and softened.
Add Broth and Potatoes: Add the chicken broth, sliced potatoes, red pepper flakes, Italian seasoning, and salt and pepper to taste. Stir everything together, ensuring that the potatoes are submerged in the liquid.
Pressure Cook: Return the cooked sausage to the pot, give it a quick stir, and lock the Instant Pot lid into place. Set the pressure release valve to "Sealing" and cook on high pressure for 8 minutes.
Quick Release: Once the cooking time is complete, perform a quick release by turning the valve to "Venting" to release the steam.
Finish the Soup: Carefully remove the lid. Stir in the chopped kale, heavy cream, and Parmesan cheese (if using). The heat from the soup will wilt the kale. Taste and adjust the seasoning as needed.
Serve: Ladle the soup into bowls and serve immediately with a side of crusty bread for dipping.