Put the chicken and stock in a crockpot on high cook for 45 minutes.
Add the onion, celery, carrots, garlic, thyme, and bay leaves, cook for 45 minutes.
Add a ½ cup flour to a cup and add a ½ cup hot water the flour stirring vigorously with a fork, this will make what is called a “slurry”.
Using a whisk slowly pour the “slurry” flour mixture to the stew mixing in until all incorporated and let it cook for 20 minutes.
Mix together the last of the flour and water in a cup to make a 2nd slurry, then add to the stew. (The consistency of the stew will be thicker when you add, so you be the judge on how thick you want the stew, add the full ½ cup or just ¼).
Add the frozen vegetables, mushroom and chicken base, then mix them together.
Reduce the heat to low and cook for 2 more hours.
Remove the thyme stems and bay leaves before serving.
Serve with warm fresh Biscuits on the bottom and ladle the stew over the top!