Cut up potatoes into bite size chunks. Place in saucepan and cover with salted water. Optionally add chopped onions.
Boil for about 20 minutes with a vented pan lid.
At end of 20 minutes, add milk.
Make dumplings: in a bowl add about a cup of flour and make a well. Pour 1 beaten egg into the well. With a fork, whisk the egg getting a little flour each time quickly to form little dumplings.
Add all dumplings to the potato soup. It will become thick very fast. Have additional milk ready to thin it out.
When it is the consistency you like, turn off the heat, put butter on top, put the lid back on and let rest about 3 minutes.