In a large pot, brown sausage over medium heat, breaking it up into small pieces with a wooden spoon. Cook sausage for about 5 minutes. Add the onions and cook until softened, about 5 minutes. Add garlic, Italian seasoning, and red pepper flakes, cook for an additional minute. Add the tomato paste and stir well to incorporate. Cook for about 3 more minutes.

Add diced tomatoes, bay leaves, and chicken stock; stir to combine. Bring to a boil then reduce the heat to low and simmer for 30 minutes. Next, add uncooked pasta and cook until al dente. Do not overcook or continue to simmer at this point because the pasta will become mushy. Stir in basil and spinach and season with salt and pepper to taste.

While the pasta is cooking, prepare the cheese mixture which you’ll sprinkle on top of the soup when serving. In a small bowl, combine the ricotta, Pecorino Romano and mozzarella cheeses; set aside.

To serve, pour the soup into bowls and add a handful of the cheese mixture to each bowl.