Warm a bit of olive oil in a large pot over medium heat. Add the Italian sausage, breaking it up as you cook, until it's fully browned, about 5 to 7 minutes. Drain any extra fat if needed.
Add the chopped onion and cook it for 3 to 4 minutes until it softens. Then stir in the minced garlic and cook for an additional minute until aromatic.
Next, toss in the diced potatoes and pour in the chicken broth. Bring everything to a boil, then reduce to a simmer and let cook until the potatoes become tender, about 15 minutes.
Stir in the chopped kale and sprinkle in red pepper flakes if you’re using them. Let it all cook together for another 5 minutes to blend the flavors.
Turn the heat to low and gently mix in the heavy cream. Season with salt and pepper to your liking and warm the soup gently for 2 to 3 more minutes.
Dish up the soup hot, and if desired, serve alongside crusty bread for a perfect finish.