Lightly season both sides of the sliced foie gras with salt and pepper.
Heat the clarified butter in a large non-stick skillet over moderately high heat, but not smoking. Sear the foie gras in batches, about 45 seconds per side. Remove from the pan and cover to keep warm.
To the fat remaining in the pan, add the shallots, apples, and nutmeg, and cook, stirring, until caramelized and tender, about 7 minutes. Remove the pan from the heat and add the Armagnac. Return to the heat and cook until the brandy is nearly all evaporated, about 2 minutes.
Divide the foie gras and apples among plates and garnish with the toasted brioche.
Yield: 8 servings