Put chicken breasts in a large pot with water, 3 stalks celery, 1/2 onion, 1 teaspoon poultry seasoning, 1 teaspoon salt, 1/2 teaspoon pepper, and Minor's chicken base. Simmer, covered, until chicken is tender. Remove chicken and let cool. Tear chicken into bite-sized pieces; set aside.
Reserve 4 cups of the broth in the pot; discard the cooked vegetables. To the broth, add the carrots, potatoes, 1/2 teaspoon pepper, 1 teaspoon salt, onion powder, and 3/4 teaspoon poultry seasoning. Cook for 10 minutes. Add 1/2 cup chopped onion, peas, and 1/2 cup chopped celery. Cook for an additional 10 minutes or until vegetables are tender; add chicken.
In a small bowl, add flour to the evaporated milk; stir into the vegetable mixture. Cook until the mixture thickens (add more flour if necessary). Adjust seasoning, if necessary. Pour the mixture into a greased 9x13" baking dish. Top with biscuit rounds, cutting some in half, if necessary, to cover top of mixture. Bake in a 400 degree oven for 25 minutes, or until biscuits are golden brown and mixture is bubbly. Remove from oven and brush tops of biscuits with butter or margarine.
In a medium bowl, stir together flour, baking powder, and salt. Cut in shortening until mixture resembles coarse meal. Add milk; mix well. Turn dough onto a lightly floured surface. Roll out to 1/2" thickness. Cut with 2-3/4" biscuit cutter. Makes 15 biscuits.