Place chicken, onion, celery, parsley, peppercorns, bay leaf, salt, and 2 cups water in a 4 quart Dutch oven. Bring to a boil over high heat, then reduce heat to low, cover, and simmer for 1 hour or until chicken is tender. Strain broth (discard vegetables) and return to Dutch oven. Cool chicken and giblets, remove meat from bones, and cut into large chunks. Discard skin and bones. Add carrots and 5 small onions to broth; cook, covered, until tender. Remove vegetables, reserving broth. Add enough water to broth to make 2-1/2 cups liquid and return to Dutch oven.

Stir in peas, mushrooms, poultry seasoning, salt and pepper, chicken, giblets, carrots, and onion. Combine flour and milk in a jar;cover and shake until blended.

Stir flour mixture into broth and cook over medium heat, stirring constantly, until mixture boils and thickens. Pour hot mixture into 2 quart casserole.

Roll out pastry to fit top of casserole. Cut slits in top. Place crust over chicken mixture and trim edge, leaving enough to fold under and form a ridge. Flute edge and brush with egg wash. Bake in preheated 400 F oven for 30-35 minutes, until crust is golden and filling is bubbly. Makes 6 servings.