Heat a large Dutch oven or heavy-bottomed pot over medium heat. Add the Italian sausage and cook for approximately 6–8 minutes, breaking it apart with a wooden spoon, until browned and fully cooked.
Transfer the sausage to a plate and set aside. Drain excess grease, leaving a small amount in the pot for flavor.
If needed, add 1 tablespoon olive oil to the pot. Add the diced sweet onion, red bell pepper, and carrots. Cook over medium heat for approximately 5–7 minutes, stirring occasionally, until the vegetables begin to soften.
Stir in the minced garlic and Italian seasoning. Cook for another 30–60 seconds, stirring frequently, until fragrant.
Add the tomato puree, chicken broth, and fresh basil. Stir until combined and bring to a gentle simmer.
Reduce the heat to low, cover, and simmer for approximately 20 minutes, stirring occasionally, until the vegetables are completely tender.
Remove the pot from the heat. Using an immersion blender, carefully blend the soup until smooth and creamy, making sure the carrots, onion, and bell pepper are completely incorporated.
Allow the soup to cool slightly until it is no longer actively bubbling. Add the whole-milk ricotta and blend again until completely smooth and creamy.
Stir in the cooked Italian sausage and drained petite diced tomatoes. Return the pot to low heat and bring to a gentle simmer. Cook for approximately 5 minutes to allow the flavors to come together.
Add the mini potato gnocchi directly to the soup. Cook according to the package directions, stirring gently and frequently, until the gnocchi are tender. Avoid overcooking.
Adjust the consistency: If the soup is thicker than you'd like, stir in additional chicken broth, approximately ¼ cup at a time, until it reaches your desired consistency.
Taste and season with kosher salt and freshly ground black pepper as needed.
Ladle into bowls and finish with freshly grated Parmesan, croutons or toasted breadcrumbs, and additional fresh basil. Serve warm.