Precook the asparagus in salted water with a little butter. White asparagus approx. 15 minutes, green asparagus approx. 8 minutes.
For the sauce, melt the butter, add the flour and cook on low heat, stirring constantly. Deglaze with the milk and bring to the boil, stirring constantly. Cook on low heat for approx. 10 minutes.
Season with salt, pepper and nutmeg to taste, and add 200 g of grated alp cheese.
Place the asparagus in a greased gratin dish and spread the sauce on top. Bake for 20 minutes at 220 degrees top heat or grill. After 15 minutes, sprinkle the remaining alp cheese over the top and allow to brown.