This recipe is approximate. One of the controlling factors is the amount of leftover mashed potatoes you have- Besides, Dad never did write this one down!
Blend flour and salt.
Make a well with the flour. Mix in the eggs, thoroughly, one at a time. Add the mashed potatoes.
You should have a dough that is not quite as stiff as a noodle dough. Add a little water, if necessary, to thin it out.
Roll the dough into long strands, about 1 inch in diameter. Cut into sections about 1 1/2 inches long.
Gently add to a large pot of boiling water. Do not add too many, nor add them too fast. You want to keep the water boiling. They are down when they start to float. Remove the floaters to a bowl, and continue till you finish off the dough pieces.
Melt butter in pan. Add coarsely sliced/diced onion. Saute to taste. I like them just transparent, Dad liked them browned, almost burnt. Salt and pepper, to taste.
You've got a few options, here-
A: Pour Onion Sauce over the whole batch B: Serve each separately, for the whiners who don't like onions. Plain butter works out, just fine.
C: As a side dish, they are great with meat gravy
Should you be fortunate to have some left over, just place in the refrigerator. They are ok, cold, but just reheat in a frying pan. They heat more evenly if you slice the kaluski into somewhat smaller pieces.