Beat all the ingredients except the butter with a wooden spoon until the batter starts to bubble. I do it with the hand mixer, it works too. Then let the dough rest for about 10 minutes.
Bring salt water to the boil and press in the spaetzle in portions using a spaetzle press or scrape it over a spaetzle board. Bring to the boil briefly, remove with a slotted spoon and rinse in cold water.
When all the spaetzle are done, drain in a colander and toss in the butter in a coated pan to warm up.