Combine the salt and flour in a large bowl or mixer.
Mix in the eggs.
Slowly mix in the water a little at a time and mix until you have a sticky, bubbly dough.
There are two methods for making the Spaetzle but in both cases, they should be prepared in batches: 1) on a small board, spread some of the dough flat and over the boiling water, use a chef's knife to cut thin strips or ribbons and push them into the water. 2) using a potato ricer or spaetzle press, take a portion of dough and extrude the spaetzle into the boiling water.
With either method, when the spaetzle float to the top, they are done, skim them off, rinse them in cold water and brown for a minute or two in a skillet with some of the sauteed onions.
In a casserole dish, layer the spaetzle, onion, and cheese as you prepare them.
Bake at 200-250 until cheese is melted (5-10 minutes).