Pour the chicken stock into a large pot over medium heat. If this is homemade stock, add salt to taste. I added almost a tablespoon of salt. Simmer the frozen chicken in the stock until it is cooked through. Remove from the stock and place on cutting board to cool slightly. Set aside the pot with the stock.
In a skillet, over medium heat, melt the butter and saute the onion and garlic until translucent. Add the chopped carrots and celery and season with salt and pepper. Cook until just barely softened. Add the vegetable mixture to the broth and bring to a simmer.
Slice the chicken (or shred, if you prefer) into bite size pieces. Add the chicken back into the soup pot and season the soup as needed. Add egg noodles and simmer just until tender. At the very end of the cooking time, add the chopped parsley. Enjoy!