Mix all of the ingredients together until very smooth. I use a food processor but a whisk, blender, or hand mixer will work well, too. The consistency of the batter should be pourable but not super runny (it should drop off a spatula or spoon in thick ribbons).
Bring a pot of lightly salted water or broth (about 2 to 3 quarts total) to a boil. Press the batter through a spaetzle maker in batches (see notes for alternate methods). Cook each batch of spaetzle for 4-6 minutes until it is puffy and rises to the top of the water/broth.
Lift the spaetzle out with a fine mesh strainer or slotted spoon (so the water/broth can be used for subsequent batches).
Saute cooked spaetzle in butter (or browned butter!) or serve plain spaetzle with stroganoff or other favorite gravy/sauce. It's also delicious tossed with butter and cheese.
Spaetzle Maker: the spaetzle maker I have is from Germany (my friend who taught me to make spaetzle gave it to me). It is similar to this one. This is another good option. If you don't have a spaetzle maker, the batter can be pressed through the holes of a colander with a spatula (just make sure to lift the colander above the boiling water so it doesn't get clogged with cooked dough). I've heard a potato ricer works well, too.