Step 1: Build the Flavor Foundation
In your slow cooker, combine the diced onion, minced garlic, chopped sun-dried tomatoes (with the reserved 2 tbsp of oil), chicken broth, Italian seasoning, dried basil, oregano, salt, black pepper, and red pepper flakes (if using). Stir to combine. Place the raw chicken thighs into the liquid, ensuring they are mostly submerged. The oil from the tomatoes will infuse the entire dish with rich, savory flavor.

Step 2: The Long, Slow Braise
Cover and cook on LOW for 6-7 hours or on HIGH for 3-4 hours. The chicken is done when it is fall-apart tender and easily shreds with a fork. The low and slow method on LOW is highly recommended for the most tender, flavorful chicken.

Step 3: Shred the Chicken and Thicken the Sauce
Using two forks, carefully shred the chicken directly in the slow cooker. In a small bowl, whisk the flour (or cornstarch) with the ¼ cup of cold water until completely smooth to create a slurry. Stir this slurry into the slow cooker. This will thicken the flavorful broth into a sauce base. Cover and cook on HIGH for 20-30 minutes, until the liquid has thickened noticeably.

Step 4: Add the Tortellini
Stir the refrigerated (or dried) cheese tortellini into the thickened sauce. Ensure the tortellini are submerged. Cover and cook on HIGH for an additional 25-35 minutes. Start checking at 25 minutes—the tortellini should be tender and cooked through. Dried tortellini may take 5-10 minutes longer.

Step 5: Create the Creamy Tuscan Sauce
Once the tortellini is cooked, reduce the slow cooker to the WARM setting (or turn it off). Stir in the room-temperature heavy cream and the grated Parmesan cheese until the cheese is melted and the sauce is smooth and creamy.

Step 6: Wilt the Spinach
Add the fresh baby spinach to the slow cooker. Gently stir until the spinach is wilted by the heat of the sauce, which will take just 1-2 minutes. The residual heat is perfect for this; no additional cooking is needed.

Step 7: Final Seasoning and Rest
Taste the sauce and adjust seasoning with additional salt and pepper if needed. Let the dish sit, covered, for 5-10 minutes to allow the sauce to thicken slightly further and the flavors to fully marry.

Step 8: Garnish and Serve
Ladle the creamy Tuscan chicken and tortellini into deep bowls. Garnish generously with fresh chopped basil or parsley and an extra sprinkle of Parmesan cheese. Serve immediately with warm, crusty bread on the side for dipping into the incredible sauce