1. Heat the olive oil and butter in a large heavy-bottomed pot over medium-high heat. Pat the chicken dry, season with 1/2 teaspoon of the kosher salt and the black pepper, then add to the pot. Sear the chicken for 4–5 minutes, stirring occasionally, until lightly golden on the edges. Transfer to a plate and set aside, leaving the drippings in the pot.

2. Reduce the heat to medium. Add the diced onion and a small pinch of salt to the same pot. Sauté for 4–5 minutes, scraping up any browned bits, until the onion is soft and translucent.

3. Stir in the minced garlic, Italian seasoning, and crushed red pepper flakes (if using). Cook for 30–60 seconds, just until fragrant, being careful not to brown the garlic.

4. Add the chopped sun-dried tomatoes and stir to coat them in the aromatics and oil. Cook for another minute so they soften and release their flavor into the base of the soup.

5. Pour in the chicken broth and water, then return the seared chicken and any juices to the pot. Add the remaining 1/2 teaspoon kosher salt. Stir well, bring to a gentle boil, then reduce to a simmer and cook for 5–10 minutes so the chicken cooks through and the flavors meld.

6. Stir in the cheese tortellini and simmer according to package directions, usually 3–5 minutes, until the pasta is just tender. Avoid overcooking, as the tortellini will continue to soften as the soup sits.

7. Lower the heat to low. Pour in the heavy cream while stirring, then add the chopped spinach. Let the spinach wilt into the hot soup for 1–2 minutes.

8. Stir in the grated Parmesan cheese until fully melted and the broth is creamy and slightly thickened. Add the lemon juice, taste, and adjust seasoning with more salt, pepper, or red pepper flakes as desired.

9. Remove from the heat. Ladle the soup into bowls and garnish with extra Parmesan and chopped fresh basil, if you like. Serve warm with crusty bread for dipping.