Beat the egg slightly. Add the salt and enough flour to make a stiff dough.
Knead well on a floured board, Invert the bowl over the dough and let stand, covered, ½ hour.
Roll out as thin as possible. Dough should not be sticky, but not too brittle.
Cut the dough into squares.
Grind the meat very finely, add the onion juice, celery, some schmaltz. Season to taste, and mix well.
Fill and pinch the ends together.
Cook in boiling salted water for 15 minutes.