1. Cut up chickens; wash; place in stock pot with celery, carrot, onion, bay leaf, thyme and salt.
2. Add enough water to cover well (about 5 cups).
3. Simmer about 1 hour, or until chicken is just cooked.
4. Remove chicken from broth; reserve broth.
5. Skin and bone chicken; cut meat into 1 or 2 inch chunks.
6. Peel potatoes and reserve in cold water to keep them from turning black.
7. Grate potatoes into a bowl of cold water.
8. When all potatoes are grated, squeeze out as much water as possible.
9. Grease a 4-cup casserole with the 2 tablespoons butter.
10. Spread 1/2 of the potatoes into bottom and sides of buttered casserole.
11. Salt and pepper to taste.
12. Place cut-up chicken pieces on top of potatoes in casserole.
13. Spread on the remaining 1/2 of the potatoes.
14. Measure out 4 or 5 cups of the reserved broth; bring to a boil; pour on the pie.
15. Dot with the 3 Tablespoons of butter, salt and pepper.
16. Bake in 400 degree Fahrenheit oven for 1-1/2 to 2 hours.