Heat a large pot or Dutch oven over medium heat. Add the sausage and cook, breaking it up with a spoon, until browned and cooked through. If there is excess grease, drain most of it; if the pan is dry, add the olive oil.

Add the onion, carrots, and celery to the pot. Cook for 5 to 6 minutes, stirring occasionally, until the vegetables begin to soften.

Stir in the garlic, Italian seasoning, and crushed red pepper flakes, if using. Cook for 30 seconds, just until fragrant.

Pour in the chicken broth and bring the soup to a gentle boil. Reduce the heat and simmer for 8 to 10 minutes, until the vegetables are tender.

Add the gnocchi and cook according to package directions, usually 3 to 5 minutes, until they float and are tender.

Stir in the heavy cream and spinach. Cook for 1 to 2 minutes, until the spinach wilts and the soup is heated through.

Taste and season with salt and black pepper as needed.

Ladle into bowls and top with grated Parmesan cheese before serving.