In a large pot or Dutch oven, cook the Italian sausage over medium-high heat, breaking it up with a spoon, until browned. Drain off excess grease.
Add the chopped onion and cook until softened, about 5-7 minutes. Stir in the minced garlic and cook for 1 minute more until fragrant.
Pour in the chicken broth and add the sliced potatoes, oregano, and red pepper flakes (if using). Bring to a boil, then reduce heat and simmer for 15-20 minutes, or until potatoes are tender.
Stir in the heavy cream and chopped kale. Cook for another 5 minutes, or until the kale is wilted and tender. Season with salt and pepper to taste.
Serve hot.
Notes
This soup is delicious served with crusty bread for dipping.