Combine all ingredients except mushrooms and butter to make spaetzle dough. Over a pot of boiling salted water, push dough through a perforated pan or colander with a flexible spatula. Little dumplings will float to the top when done, no more than 1 minute. Remove with a perforated spoon or hand strainer and set aside. Saute mushrooms in 1 tablespoon of the butter about 2 minutes. Melt remaining butter in a separate pan, add spaetzle and saute until lightly browned. Combine with mushrooms, season and serve.