Butter a small, rectangular
gratin dish.
Place a single, tight layer of
celeriac on the bottom of the dish. Sprinkle the layer lightly with
salt,
pepper, and
nutmeg.
Place a single, tight layer of
apple slices on top of the layer of
celeriac. Continue layering the
celeriac, seasonings, and apples until the dish is full. Finish with a layer of
celeriac on top.