Prepare a "Bordelaise" Sauce as previously described. The diluent of this sauce must be an excellent red wine. For one pint of sauce, pass four raw duck's livers through a sieve; add the resulting puree to the Bordelaise and heat the latter for a few minutes in order to poach the liver. Be careful, however, not to heat the sauce too much or too long, lest the liver be cooked. Serve this sauce with duckling á la Rouennaise.