Heat a large Dutch oven or heavy-bottomed pot over medium-high heat. Add the Italian sausage and cook, breaking it up with a spoon, until browned and cooked through, about 5-7 minutes. Use a slotted spoon to transfer the sausage to a paper towel-lined plate, leaving about 1 tablespoon of drippings in the pot. If there isn't enough, add the olive oil.

Add the diced onion to the pot and sauté over medium heat until softened and translucent, about 5 minutes. Stir in the minced garlic and cook for another minute until fragrant.

Pour in the chicken broth, scraping up any browned bits from the bottom of the pot. Add the diced potatoes, dried oregano, and red pepper flakes (if using). Bring the soup to a boil, then reduce the heat to maintain a steady simmer.

Cover and let the soup simmer for 10-15 minutes, or until the potatoes are fork-tender.

Reduce the heat to low. Return the cooked sausage to the pot. Slowly stir in the heavy cream. Be careful not to let the soup boil after adding the cream to prevent it from curdling.

Stir in the chopped kale and cook for 2-3 minutes, just until the kale has wilted to a vibrant green. Season generously with salt and black pepper to taste.

Ladle the hot soup into bowls. Garnish with shredded Parmesan cheese and fresh parsley if desired, and serve immediately.