1. Peel and cut the apples into quarters. In a saucepan, melt the butter. Add the apples and cook for 5 minutes.
2. Cut the celeriac into slices. Blanch the celeriac and the stalks of celery for 8 minutes in a pot of salted water. Drain. Cut the celery into slices.
3. Preheat the oven to 375°F.
4. In a bowl, beat the eggs and cream. Season with salt and pepper.
5. In a gratin dish, place layers of celeriac, celery, and apples. Add the egg-cream mixture.
6. Cover with cheese. Bake for 10 minutes. Remove from the oven and serve hot.