Mix the flour, salt and eggs together in a bowl (by hand or with a mixer). Slowly stir in the lukewarm water until a slightly tough dough is formed. You can tell if you pull a wooden spoon through the dough and give the mass a slight resistance. Then let the dough stand for about 15 minutes and then stir again briefly, the glue in the flour still pulls and solidifies a little, possibly add 1 - 2 teaspoons of water.
In the meantime, heat about 2 liters of water in a saucepan and add salt. Prepare a bowl for the finished spaetzle, add a little butter. Only when the water is boiling, fill the dough into the spaetzle slicer and slice it straight into the boiling water. Bring to the boil briefly when the spaetzle come to the top, lift out immediately with the slotted spoon and place in the bowl. Repeat the process until all of the batter is used up.
Place the spaetzle in the warm oven to keep it warm. When all the spaetzle are ready, serve immediately.