For the dough, mix the flour with the eggs, salt and 200ml water to form a dough. Leave to stand for 15 minutes.
Finely grate the cheese.
Peel the onions, cut in half then into thin strips.
In a frying pan, melt 2 tbsp butter and fry the onions until golden. Season with salt and pepper and keep warm.
Bring a large pan of salted water to the boil. Place the spaetzle grater on the top edge and fill with a portion of dough. Move the slider slowly and evenly so that the spaetzle fall into the boiling water.
Boil for 2-3 minutes, remove and drain. Repeat to use up all the dough.
In a pan, melt the remaining butter. Add the spaetzle gradually, sprinkling with the cheese.
Turn the spaetzle several times. Add half the onions and mix.
Add the remaining onions to the spaetzle. Season lightly with pepper and nutmeg and serve in the pan.