Whisk together the egg yolks, chicken stock, chicken fat, parsley, and salt. Stir in the matzo meal. In the bowl of an electric mixer with a whisk attachment, whip the egg whites with a pinch of salt until they are stiff. Whisk them into the matzo mixture until it is smooth. Refrigerate for at least 15 minutes, or until the mixture is thick.

Form balls the size of golf balls by shaping them with 2 spoons, rolling them with your hands, or scooping them with a small ice cream scoop. Drop them into simmering chicken stock and cook for 30 minutes, or until fully cooked and puffed, turning once. Remove and serve hot in chicken soup