- Preheat oven to 180° C (350° F).
- Fill a large pot with salted water and cook the potatoes. Drain.
- Put the potatoes in a large bowl and mash. Add the cheese, sour cream, and maple syrup. Season well with salt and pepper.
- Butter a large oven-proof dish and put in the mashed potato mixture, spreading evenly.
- Lightly beat the egg and brush the potato mixture with it.
- Cover with a layer of breadcrumbs, dot with knobs of butter, and bake for about 30 minutes.