1. Waiting is part of the art of the terrine: Before beginning to clean and devein whole foie gras, allow chilled foie gras to warm up so that it's tender and manageable (cold liver is brittle, and its veins harder to locate and remove intact). Pull any bits of translucent membrane from the surface, and separate the two lobes, using a knife to sever any connecting veins. Inspect the folds for patches of bitter green bile that could mar the terrine and extract them with a knife.
2. Cleaning and deveining is a tricky business. For a smooth terrine, you must remove the thick, branched main vein that runs through the center of each lobe. If you're experienced, dig into the middle of each lobe with a paring knife, catch the vein under its tip and pull it out. If you're a novice, probe for the vein and its branches with your fingers, pulling it out as you follow its length.
3. Soaking deveined foie gras pieces overnight in ice water draws out any excess blood.
4. The next day, break the liver into pieces and marinate it for 2 hours in sauternes.
5. Cooking the foie gras in a bain-marie renders a good deal of fat. This fat is precious, both for flavoring and preserving the terrine. Save excess fat and refrigerate. To store terrine, pour melted fat over foie gras to seal it.