Split the kidneys lengthwise, leaving enough meat and skin on one side to serve as a hinge. Rub well inside with melted butter, and broil them, back downward, over a bright fire for eight minutes. Have ready a stuffing of bread-crumbs, cooked salt pork, parsley and butter, seasoned with pepper, salt, and onion-juice. Heat in a saucepan set in another of boiling water, stir in the juice of half a lemon, fill the kidneys with the mixture, run a toothpick through the outer edges or lips to keep in the stuffing, pepper them and serve. Send around sauce piquante with them.