Chop the onion and sautée on low heat in the oil or fat until translucent, about 5 minutes.
Whisk the eggs lightly. Grate the bread in a food processor.
Put every ingredient in a bowl, except the breadcrumbs. Mix everything well. (Season with paprika and/or minced garlic according to your taste.)
Pour the breadcrumbs in a plate. Wet your hands and make nice little balls. Roll them in the breadcrumbs so it will cover them evenly.
Heat the oil in a large frying pan. Fry both sides until cooked through. My ping pog ball sized meatballs are perfect after 4-5 minutes, larger ones might need 10-12 minutes.