Brown the Italian sausage in a large Dutch oven or soup pot over medium heat, breaking it into crumbles as it cooks.
Drain most of the excess grease, leaving a small amount in the pot for flavor.
Add the diced onion and cook for 4–5 minutes, stirring occasionally, until softened.
Stir in the minced garlic and Italian seasoning, then cook for about 30 seconds, until fragrant.
Add the diced Yukon Gold potatoes, chicken broth, and browned sausage.
Stir everything together.Bring the soup to a gentle boil, then reduce the heat and simmer for 15–20 minutes, or until the potatoes are fork-tender.
Lower the heat and slowly stir in the heavy cream.
Add the fresh spinach and cook for 2–3 minutes, until the spinach has wilted.
Season with salt and black pepper to taste, then serve hot.
