Peel and wash the potatoes, cover and cook in salted water for about 20 minutes. Drain potatoes and let them cool down a little.
Cut the bacon into strips and fry them crisply in a pan without fat. Remove. For the béchamel sauce, heat 2 tablespoons of butter in the bacon fat. Dust with flour and sauté lightly while stirring. Add 1⁄4 l water and milk and bring to the boil.
Simmer for about 5 minutes while stirring. Season sauce with salt, pepper and nutmeg.
Grate the cheese roughly. Clean and wash spring onions and cut into fine rings. Peel, quarter, core and cut pears into thin slices.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Cut the potatoes into slices, mix with spring onions, pears and bacon. Put them into a greased casserole dish. Pour sauce over it and sprinkle with cheese.
Bake in a hot oven for about 30 minutes.