Cover and poach chicken in stock until tender, about 15 to 20 minutes. Cool in broth; reserve broth. Remove skin from chicken and bone. Cut chicken in bite-size cubes and set aside.
Topping:
*Melt butter in a large skillet; add celery and onion and sauté until transparent. Blend in chicken stock, sage, and prepared stuffing. Add salt and pepper to taste. Set aside.
Vegetables:
*Toss together in bowl. (Peas do not need to be cooked.)
Sauce:
*Blend all ingredients together; set aside.
Heat oven to 350° F. In a 9 x 13-inch shallow baking dish, layer 2/3 of the topping; cover with chicken and vegetables. Pour sauce over all. Sprinkle remaining stuffing mixture on top. Cover and bake 30 minutes or until hot and bubbly.