In a bowl whisk together eggs, milk, Grand Marnier, and 2 tablespoons oil or butter until combined well and gradually whisk in flour. Stir in sugar and zests and chill, covered, 30 minutes. Preheat oven to 200°F. Gently stir batter. Heat a well-seasoned 7-inch crepe pan or not-stick skillet over moderate heat until hot and brush lightly with some melted butter. When butter starts to bubble remove pan from heat. Half fill a 1/4-cup measure with batter and pour into pan, tilting and rotating pan quickly to evenly coat bottom. Return pan to heat and cook pancake until underside is golden brown. Turn pancake and cook until underside is golden brown, transferring to a heatproof platter. Make more pancakes in same manner with remaining batter and butter, keeping pancakes warm in oven. Pancakes may be made ahead and kept, wrapped well in plastic wrap, chilled 2 days or frozen 2 weeks. Reheat pancakes, wrapped in foil, in oven before filling them.