Put flour, salt and nutmeg in a bowl, make a well and break the eggs there. Mix well by adding water little by little.
Boil salted water in a saucepan. Hold the strainer over spaetzle your pan, pour the batter and scrape. When the spaetzle rise to the surface, they are cooked.
Fry the onion in a pan with butter, add the drained spätzles and cheese.