Cook potatoes in water until tender. Cover and refrigerate 12 to 24 hours. Finely chop or mash cooked potatoes. In a medium bowl, combine potatoes, eggs, salt, flour, and nutmeg to form a firm but light paste. If mixture is too wet, add flour as needed. Melt butter in a skillet, then saute bread cubes until golden brown. Working with well-floured hands, form the smooth paste into a roll about 2 1/2 inches in diameter. Cut roll into 8 or 10 pieces. Form pieces into dumplings, enclosing a few cooked bread cubes into their centers. Bring a large kettle of salted water to a boil. Add dumplings (a few at at time) to the water. Do not over-crowd. Simmer about 15 minutes. Dumplings are done when they begin to float. Remove from water with a slotted spoon and drain well. Serve immediately.