In a large pot, melt the butter over medium heat.
Add celery, grated onions, and minced garlic; sauté for 1-2 minutes until celery starts to soften.
Whisk in the flour until well combined and cook for another minute.
Gradually add the water and stir in the chicken bouillon cubes until dissolved.
Add cooked chicken, thyme, and nutmeg; stir well and bring the mixture to a boil.
Reduce heat and simmer for 15 minutes to develop flavors.
In a separate saucepan, gently warm the heavy cream.
Add the warmed cream, spinach, and gnocchi to the soup pot.
Simmer for an additional 15-20 minutes, or until the gnocchi is tender and spinach is wilted.
If the soup needs thickening, mix cornstarch with cold water and stir into the soup. Cook for a few more minutes until thickened.
Adjust seasoning if needed, then serve warm and enjoy your hearty chicken gnocchi soup!