In a large pot, heat the butter and oil over medium heat. Add in the onion, garlic, carrots, and celery. Season with salt and pepper and cook until tender, about 10 minutes
Add in the flour and stir into the vegetables, cook for 3 minutes, stirring often
Stir in chicken broth, followed by ½ and ½
Add in the chicken, bring to a simmer and maintain for 20 minutes, stirring often
Season with salt and pepper to taste
Cook the gnocchi in a separate pot according to the package, add them to the soup with the spinach