How to Make It
Line an 8-by-4-inch glass or ceramic loaf pan with 4 layers of plastic wrap, leaving a 4-inch overhang all around.
Using your hands, gently pull open each lobe of foie gras at its natural separations and remove the network of veins with a thin sharp knife; if the lobes break apart, the pieces can be pressed back together. Set the foie gras in a large baking dish and pour the Sauternes and port over it. Cover with plastic wrap and refrigerate for 2 hours.
Drain off the marinade from the foie gras, season generously with salt and pepper, then sprinkle with the nutmeg. Arrange one of the foie gras lobes in the prepared loaf pan, set the second lobe on top and press firmly to pack the 2 lobes together in the pan. Cover with the overhanging plastic wrap, then cover the pan tightly with foil.
Set the loaf pan in a small flameproof roasting pan and add enough water to the pan to reach three-quarters of the way up the sides of the loaf pan. Remove the loaf pan and bring the water to a simmer on the stove. Return the loaf pan to the water and simmer gently over low heat until an instant-read thermometer inserted in the foie gras registers 130°, about 15 minutes. Transfer the terrine to a rack and let cool to room temperature. Remove the foil. Top the terrine with another loaf pan weighted down with canned goods and refrigerate for at least 24 hours.
Melt the butter in a large skillet. Add the apple wedges and toss to coat. Sprinkle with the sugar and cook over moderate heat until browned on the bottom, about 4 minutes. Raise the heat to high, turn the apples and cook until browned on the bottom but still slightly crisp, about 3 minutes.
Unwrap and unmold the terrine onto a platter. To serve, run a thin sharp knife under hot water and wipe dry. Cut the terrine into 1/2 -inch-thick slices, rinsing the knife under hot water and drying it between cuts; hold the slice together as you cut. Set a foie gras slice on each plate and serve with the sautéed apple wedges and toasted Walnut Bread.