Heat a Dutch oven over medium-high heat, then brown the Italian sausage with the diced onion and minced garlic until the sausage is cooked through. Drain excess fat so the soup stays creamy, not greasy.

Reduce heat to medium, add the butter and flour, and whisk for 1 minute until smooth and lightly bubbling. Slowly whisk in the chicken broth so no lumps form.

Pour in the heavy cream, add Italian seasoning and a pinch of nutmeg, then bring the mixture to a simmer. Keep it at a gentle simmer for 2–3 minutes to thicken slightly, stirring often.

Add the broken white lasagna noodles and cook for 12–14 minutes, stirring occasionally, until tender. Keep the soup at a steady simmer so the noodles cook through.

Stir in the baby spinach and cook for 1–2 minutes until wilted into soft ribbons. Turn off the heat once the spinach is fully wilted.

Ladle the soup into bowls, then top each bowl with ricotta, shredded mozzarella, and grated parmesan. Broil for 2 minutes until the cheese is melted and lightly golden, or serve as-is if you skip broiling.

Finish with fresh basil over the top right before serving for a bright, herbaceous note. Serve immediately while the noodles are hot and the cheese is molten.