Place the bread strips in a bowl and pour in about 1 cup of lukewarm water, cover with a dish cloth. Peel and dice the onion.
Knead the ground meat with the eggs, parsley, and the softened bread. Season with salt and pepper. With damp hands, form the mixture into about 8 balls, then flatten them partially.
Heat the vegetable oil in a large pan and brown both sides of the meatballs well. Turn the heat down to medium and fry for another 10 or 15 minutes, adding the butter during this time.
Remove the meatballs from the pan and let them drain on paper towels. Best served with potato salad, rolls, and mustard.