Melt the butter in a large pot over medium heat. Add the onion, celery, and carrots, and saute for 7-8 minutes or until the onion turns translucent.
Add the minced garlic, dried thyme, parsley, and onion powder, and sauté for 1 minute, until fragrant.
Stir in 9 cups of chicken broth, along with the salt and pepper. Stir well, bring to a simmer, and cook with the lid ajar for 10 minutes.
While the soup simmers, cook the egg noodles in a pot of heavily salted water according to the package directions. Drain the noodles and set aside.
Whisk the cornstarch into the remaining cup of chicken broth until well combined. Add the chicken broth mixture, chicken, and cooked noodles to the pot, bring back to a simmer, and cook for 1-2 minutes or until the soup has slightly thickened and the chicken is heated through.
Stir in the chopped parsley and season the soup to taste with salt and pepper. Serve the soup hot!