Soak the bread cubes: Cut the stale bread into cubes and place in a bowl. Warm the milk and pour it over the bread. Let soak about 10 minutes.
Fry the onion: In a small skillet, sauté the onion in butter over medium heat until translucent. Add to the soaked bread along with the eggs, salt, nutmeg, and parsley.
Make the dough: Mix everything until a uniform mass forms. If the mixture seems too soft or won’t hold together, stir in a little breadcrumbs to bind.
Shape into a roll: Form the dough into a long roll.-Cloth method: Place on a damp, clean kitchen towel, roll up tightly, and tie the ends like a candy wrapper.-Plastic + foil method: Wrap snugly in plastic wrap, then in aluminum foil, sealing the ends well. Cook: Bring a large pot of water to a gentle simmer (not a rolling boil). Place the wrapped roll in the water and cook 30–40 minutes.
Serve: Remove, unwrap carefully, and slice into rounds. Serve immediately—traditionally with roast meats, goulash, creamy mushroom ragout (Rahmschwammerl), or game dishes.