1. Melt the butter with the olive oil in a large heavy-bottomed pot or Dutch oven over medium heat. Add the onion, carrots, and celery, and cook, stirring occasionally, until the vegetables begin to soften and the onion turns translucent, about 5 to 7 minutes.

2. Stir in the minced garlic, Italian seasoning, dried thyme, red pepper flakes (if using), salt, and black pepper. Cook for about 1 minute, just until the garlic is fragrant.

3. Sprinkle the flour over the vegetables and stir well to coat. Cook for 1 to 2 minutes, stirring constantly, to cook off the raw flour taste and form a thick paste.

4. Slowly pour in the chicken broth while whisking or stirring vigorously to avoid lumps, scraping up any browned bits from the bottom of the pot. Bring the mixture to a gentle simmer and cook for about 5 minutes, allowing it to thicken slightly.

5. Add the shredded chicken, then pour in the whole milk and heavy cream. Stir until everything is well combined and return to a gentle simmer, keeping the heat low so the dairy does not boil.

6. Add the cheese tortellini and cook according to the package directions, usually 4 to 6 minutes, until the pasta is tender and cooked through, stirring occasionally.

7. Stir in the frozen peas, chopped spinach, Parmesan cheese, and lemon juice. Simmer for another 2 to 3 minutes, just until the peas are heated through, the spinach is wilted, and the cheese has melted into the broth.

8. Taste and adjust the seasoning with more salt and pepper if needed. Ladle the soup into bowls and serve hot with extra Parmesan and freshly cracked black pepper on top.