Cook the potatoes: Place the unpeeled potatoes in a large enough pot and cover with cold water. Bring to a boil with the lid on. Once boiling, add about 1 tablespoon of salt, reduce to medium heat so the water is just gently boiling, and cook for about 30 minutes until a knife slides through easily. Drain and let them steam for a moment.
2 lbs yellow potatoes
Rice the potatoes: Push the hot potatoes through a potato ricer into a large bowl (the peel stays in the ricer; remove it between each potato). Spread out the riced potatoes so they don't clump together, and let them cool for 15 minutes.
Make the bread filling: Melt butter in a pan over medium heat. Cut the bread into small cubes (about ½ inch) and sauté until golden. Set aside.
2 tablespoons butter, 1 slice white bread
Make the dough: Add the egg, three-quarters of the potato starch, salt, and nutmeg to the bowl. Knead with your hands until the dough comes together smoothly; don't overknead the dough. If it's too sticky, knead in more potato starch.
1 egg, 1 cup potato starch, 1½ teaspoons salt, ⅛ teaspoon nutmeg
Shape the dumplings: Bring a large pot of water to a boil, add salt and then reduce to just below simmering (no bubbles). Meanwhile, with wet hands, divide the dough into 10 portions (about 100 g each). Roll into a ball, flatten each piece in your palm, place a bread cube in the center, and roll into a smooth, round ball.
Cook the dumplings: Do a test dumpling first if this is your first time. Gently lower the dumplings into the hot (not boiling) water. Cook uncovered for about 20 minutes, stirring gently in the first couple of minutes so they don't stick to the bottom. They are done when they float to the surface and spin easily when nudged.
Serve: Remove the dumplings with a slotted spoon and serve immediately.