Heat the olive oil in a large pot over medium heat. Once shimmering, add the diced onion and cook for 2-3 minutes, stirring occasionally, until softened and fragrant. Add the garlic and cook for another minute until it becomes aromatic. This foundation of caramelized aromatics will build the depth of flavor for your entire soup.

Increase heat to medium-high and add the Italian sausage to the pot with the cooked aromatics. Break it apart as it cooks, creating small crumbles throughout. Cook for 5-7 minutes until the meat is fully browned and no longer pink. Carefully pour off excess grease from the pot, leaving just enough for flavor—I find that leaving about a teaspoon of fat adds richness without being greasy.

Pour the chicken stock into the pot with the browned sausage and aromatics, scraping the bottom to release any flavorful browned bits. Add the diced tomatoes with their juices, tomato paste, oregano, Italian seasoning, and red pepper flakes. Stir well to combine and bring the mixture to a boil over medium-high heat. The tomato paste needs to dissolve fully into the broth to develop a rich, cohesive sauce.

Once the broth reaches a boil, add the broken lasagna noodle pieces directly to the pot and stir immediately to prevent sticking. Reduce heat to medium and simmer for 8-10 minutes, stirring occasionally, until the noodles are tender and have absorbed some of the broth. The soup should have a hearty consistency at this point—neither too brothy nor too thick.

Remove the pot from heat and stir in the parmesan cheese until fully melted and incorporated. Gently fold in the mozzarella cheese, allowing it to melt slightly into the hot soup—this creates those creamy ribbons throughout without completely melting it into invisibility. Taste the soup and season with salt and pepper to your preference, remembering that the broth and cheeses already contain saltiness.

Ladle the soup into bowls and top each serving with a generous sprinkle of the freshly chiffonade basil. The fresh herb cuts through the richness of the cheese and adds a bright, aromatic finish that makes this soup feel complete. I prefer to add basil at serving time rather than cooking it in the pot—the fresh flavor and delicate texture are best preserved when added just before eating.