Using sharp knife or food processor, mince large onion, celery stalks, carrots, and garlic (if using fresh) into small pieces.
Place 4 Tbsp of butter and minced vegetables in a large soup pot over medium-high heat. Sautee vegetables, stiring occasionally, for 2-3 minutes until butter is melted and onions are transluscent.
Sprinkle sauteed vegetable mixture with 1/4 c GF flour and stir to lightly coat all vegetables with the flour, just a few seconds.
Stir in 2 cups of chicken broth. Allow to simmer for 2-3 minutes, stiring occasionally.
Add bay leaf, garlic powder (if not using fresh), a sprinkle of cayenne, Italian seasoning, freshly ground salt and pepper.
Soup consistency should be very thick after simmering at medium-high heat. Add 5 more cups chicken broth, stiring to combine.
Add shredded chicken to the soup and raise heat to high, stiring occasionally, to rethicken. This should only take a few minutes, stiring as the soup reaches boiling temp. Add additional cup of chicken broth if soup is thicker than you prefer.
Reduce heat to medium, allowing soup to simmer while you prepare the strip dumplings.