In a large skillet, heat up the chicken stock on medium until it comes to a boil. While you are waiting for the chicken stock to come to a boil, whisk together the milk and flour in a small bowl until there are no flour clumps.Add in the milk/flour mixture to the boiling chicken stock and whisk on medium heat for about 5 minutes.Add in the garlic powder, onion powder, thyme, salt, and pepper. Whisk together.You can use it right away in soups or casseroles.Allow the condensed soup to cool before transferring to a container (mason jar).