In a large, shallow bow whisk eggs. Mix together sugar and nutmeg, whisk into eggs, and add milk, juice and zest.
Heat 2 saute pans, preferably nonstick, over medium heat; heat oil in one pan. Dip bread slices in egg mixture until thoroughly moistened. Carefully transfer to oiled pan and cook until golden brown, 2 to 3 minutes per side, turning once. Season foie gras with salt and pepper and sear until a brown, crusty edge forms on each side, about 1 minute per side. Transfer toasts and foie gras slices to warmed plates. Arrange 1 slice foie gras on each toast; dust very lightly with powdered sugar; drizzle with vinegar and drizzle caramel sauce in a pattern around rim of plate. Serve immediately.
Yield: 4 appetizer servings