Whip the flour, eggs, water and salt to a smooth dough. Leave the dough to swell for at least 30 minutes.
In the meantime, cut the onions into fine slices and fry them in a hot pan with the butter until golden brown. Keep warm.
Bring water and salt to the boil in a large pot. Put the finished spaetzle dough through a spaetzle press into the boiling water. When the spaetzle are cooked, skim them off the surface of the water.
Place the finished spaetzle alternately with the grated Emmental (or mountain cheese) in an ovenproof form/bowl or rustic pan. Start with spaetzle and finish with a layer of cheese.
Then bake the cheese noodles for 15 minutes at 180° C top/bottom heat in a preheated oven. Finally, sprinkle the fried onions on top and garnish with some parsley if necessary. Serve immediately.
A green salad goes well with it.