1 tablespoon olive oil
1 small onion, diced
3 stalks celery, diced
3 cloves garlic, minced
2 carrots, shredded
1 pound cooked, cubed chicken breast
4 cups chicken broth
1 (16 ounce) package mini potato gnocchi
1 (6 ounce) bag baby spinach leaves
1 tablespoon cornstarch (optional)
2 tablespoons cold water (optional)
2 cups half-and-half cream
salt and ground black pepper to taste