Add salt and eggs to mashed potatoes and combine farina and flour. Mix and knead. Roll out dough and cut into 15 squares; wash, pit and dry plums. Place half teaspoonful of sugar in center of each plum. Place plum in center of each square and fold dough around plum so that it is completely covered. Drop into boiling, salted water and cook for 20 minutes. Drain and serve topped with buttered bread crumbs.