I start by adding the celery, carrot, onion, parsley, garlic, thyme, salt, pepper, and broth straight into the slow cooker and give it all a good stir. Then I nestle the chicken breasts right into the liquid so they're fully submerged. This step takes me all of five minutes before I walk away.
I cover the slow cooker and set it to low for 6 to 7 hours, or high for 3 to 4 hours if I'm short on time. The vegetables turn tender and the chicken cooks through gently, which keeps it from drying out the way stovetop cooking sometimes can.
Once the chicken is fully cooked, I shred it right in the slow cooker using two forks, though you can also pull it onto a cutting board if that's easier for you. This is the point where the kitchen really starts to smell incredible.
I whisk the heavy cream and corn starch together separately first so there are no lumps, then stir that mixture into the soup along with the gnocchi. I cover it again and let it cook on high for about an hour, until the gnocchi is tender and the broth has thickened up nicely.
Right before serving, I stir in the fresh spinach and grated Parmesan. The spinach wilts almost instantly in the hot broth, and the Parmesan melts in to give the soup that final creamy, savory finish. I taste and adjust the seasoning one last time before ladling it into bowls.