Cook potatoes in water until tender. Cover and refrigerate 12 to 24 hours. Peel and finely chop cooked potatoes or mash thoroughly. In a medium bowl, combine potatoes, flour, eggs, salt and nutmeg to form a firm, but light paste. If mixture is too moist, add flour as needed. This will keep the dumplings from falling apart during cooking. Melt margarine in large skillet. Add bread cubes and sauté until golden brown. Working with floured hands, form potato paste into a roll about 2 1/2 inches in diameter. Cut roll in 8 to 10 pieces. Form pieces into dumplings enclosing a few sautéed bread cubes in center of each dumpling. Bring a large pot of salted water to a boil. Add dumplings, one at a time, and simmer about 15 minutes. Dumplings are done when floating on top. Remove dumplings with slotted spoon drain well.