Method
Cook onion in 1 tablespoon butter over low heat just until it begins to soften. Remove from heat.
Soak bread in milk for five minutes. Squeeze to remove all excess liquid.
Mix bread into ground meet. Add salt, pepper, onion and egg yolk. With clean hands mix thoroughly, but try not to overmix.
Wash meat residue from hands. With moist palms, shape into about 16 meatballs.
Put flour on a plate and roll meatballs lightly in the flour. Shake off any excess as it will get gummy in the cooking.
Melt remaining 2 tablespoons butter in a large saute pan. Put in meatballs and flatten slightly. Fry 5 - 7 minutes on each side, or until slightly pink at the center.
Sour Cream Sauce: