Take four veal sweetbreads, soak them for an hour in cold salted water, first removing the pipes and membranes; then put them into boiling salted water with a tablespoonful of vinegar, and cook them twenty minutes, then drop them again into cold water to harden. Now remove them, chop them very fine, almost to a paste. Season with salt, pepper and a teaspoonful of grated onion; add the beaten yolks of three raw eggs, one tablespoonful of butter, half a cupful of cream, and sufficient fine cracker crumbs to make stiff enough to roll out into little balls or cork-shaped croquettes. Have ready a frying kettle half full of fat over the fire, a dish containing three smoothly beaten eggs, a large platter of cracker dust; wet the hands with cold water and make the mixture in shape; afterwards rolling them in the cracker dust, then into the beaten egg, and again in the cracker dust; smooth them on the outside and drop them carefully in the hot fat. When the croquettes are fried a nice golden brown, put them on a brown paper a moment to free them from grease. Serve hot with sliced lemon or parsley.