Preheat oven to 350° F. Generously butter a 1-1/2 quart baking dish. Set aside. Cook potatoes in water until soft enough to mash. Mash and beat in milk, salt and pepper. Transfer to large bowl. Melt the 8 tablespoons of butter in large skillet over medium heat. Add onions and celery; cook until just soft, about 10 minutes. Add to potatoes, using slotted spoon. Sauté bread cubes in same skillet until brown and crispy, adding more butter if needed. Transfer bread to potatoes. Add the eggs, parsley, salt and pepper to potato mixture. Mix thoroughly; transfer to baking dish. Dot the casserole with butter bits. (Casserole can be prepared up to 2 days ahead, refrigerated, and brought to room temperature before continuing.) Bake in oven until hot, about 35 minutes. Cover with foil if top browns too much.
Serves: 4-6