Heat olive oil in a large skillet over medium-high heat. Once shimmering, add the turkey sausage rounds and brown them for 3-4 minutes, stirring occasionally, until they develop a golden crust on the outside. This browning step builds flavor through the Maillard reaction, creating a deeper, richer base for your soup. Don't worry about cooking them through—they'll finish cooking in the slow cooker.

In the same skillet (don't clean it—those browned bits add tremendous flavor), add the diced onion and sauté for 2-3 minutes until it starts to soften and become fragrant. Mince the garlic cloves and add them to the pan, cooking for another 30 seconds until aromatic. Stir in the Italian seasoning, salt, pepper, and red pepper flakes, toasting the spices for about 15 seconds. This brief toasting releases the essential oils in the dried herbs, making them more flavorful throughout your soup.

Transfer the browned turkey sausage and the aromatic mixture from Step 2 into your slow cooker. Add the diced tomatoes (with their juices) and chicken broth, stirring well to combine all ingredients evenly. I find it helpful to give everything a good stir to make sure the spices are distributed throughout the liquid. Cover and cook on high for 4 hours or low for 8 hours—both methods will give you tender, deeply flavored soup.

About 30 minutes before your slow cooker finishes, add the tortellini directly to the simmering soup and stir gently. The tortellini will cook through in this time without falling apart or becoming mushy. This timing is crucial—adding it too early results in soggy pasta, while adding it at the end means you'll be waiting for it to cook before serving.

Once the tortellini is tender, turn off the slow cooker and stir in the heavy cream, mixing it thoroughly into the hot soup until well combined. Add the fresh spinach in handfuls, stirring gently as it wilts into the soup—this should take just 1-2 minutes. The residual heat will wilt the spinach perfectly without overcooking it, keeping it bright green and nutritious. I always add the cream at the end rather than earlier because heating it for hours can cause it to break down and lose its velvety richness.

Ladle the hot soup into bowls and serve immediately. The soup is rich and warming, perfect on its own, though you can add crusty bread on the side if desired.