Put about a pint of water in a saucepan large enough to hold the lobster. Add the salt and peppercorns, onion, carrot and herbs tied in a cheesecloth bag. Bring to a boil and add the lobster and simmer, covered, for 15 minutes. Discard the spice bag, and set the lobster aside to cool. Strain the stock, and return it to the heat with the chicken stock and the bread. Stir together until the bread has dissolved in the stock. Remove the lobster meat from the shell, and cut up, reserving some of the larger pieces to garnish the soup. Mash the liver with the butter and add to the soup, along with the rest of the lobster meat, the cream, and sherry or Madeira to taste. Serve hot.