Combine onion, carrots, celery, and garlic in the bowl of your slow cooker. Season chicken on both sides with salt and pepper and place on top of vegetables. Add thyme and rosemary, then pour in chicken broth. Cook on high for 4 to 5 hours or low for 7 to 8 hours.
Remove chicken and rosemary sprigs from slow cooker and discard rosemary. Using 2 forks, shred chicken, then return chicken to soup. Remove about ¼ cup of hot broth and place in a medium bowl. Add cornstarch to broth and whisk to combine, then pour back into soup. Add cream and gnocchi, cover, and cook 45 minutes more on high.
Stir spinach into soup until wilted. Season to taste and serve with freshly ground black pepper.
Recipe by 5* trending recipes with videos at https://food.theffeed.com/2019/11/19/slow-cooker-creamy-gnocchi-soup/