Bake pie shells according to package instructions. Once cooled, break into bite size pieces to sprinkle on top of soup.
In a large stock pot, melt butter and cook onions, carrots and celery over medium heat until softened.
Sprinkle in flour and cook about one minute more.
Add chicken stock and increase heat to medium high.
Once chicken stock begins to simmer, add hash browns and let simmer for about 15 minutes, or until potatoes begin to break down and thicken soup.
Add chicken and let simmer until heated through, then add heavy cream and frozen peas and let simmer about 5 more minutes.
Add salt and pepper to taste, and adjust consistency of soup with additional chicken stock if needed.
Sprinkle with flat leaf parsley and serve with pie shell pieces.