Peel potatoes and celery knobs and cut them into even slices about one-eighthinch thick.
Butter a baking dish well and arrange alternate layers of celery knob, potato, and cheese, using about onecup of the cheese. Begin and end the layers with potatoes. Sprinkle with salt and pepper and pour the stock over all.
Bake for one to one and one-quarter hours, until potatoes are tender and most of the liquid is absorbed. Sprinkle with remaining cheese and return to the oven until cheese melts.