Preheat oven to 350 degrees. In a large pot bring salted water to a boil. To make your sauce, In a small bowl combine garlic powder, celery salt, crushed rosemary, and minced onion. Set aside. In another bowl prepare a slurry by adding milk to your flour. Whisk until the flour dissolves completely. In a small sauce pan boil 1 1/2 cups chicken broth. When the broth comes to a boil slowly add the slurry to the broth, followed by the spices, and continue whisking until the mixture is thickened. (about a minute or two) Reduce heat to low and whisk for about one more minute. In a large bowl add the sauce, light sour cream, remaining chicken broth, frozen vegetables, and shredded chicken. Stir until combined. Boil noodles according to package, drain, and add to a 9x13 pan or large casserole dish. Pour chicken mixture over the noodles and mix until combined well. Add crushed crackers evenly on top, cover with tin foil, and bake for about 25 minutes.