In a medium bowl, beat the 3 eggs and milk until well blended. Add the flour and salt; stir until batter is barely blended (the batter should be slightly lumpy).
In another bowl, toss apple slices with sugar, 2 tablespoons of lemon juice, and cinnamon.
Melt unsalted butter in a heavy, ovenproof 12-inch cast-iron or non-stick skillet over medium-high heat. Add apple mixture and saute 4 minutes, or until slightly softened. Spread out apples into an even layer; pour batter over apples.
Bake in preheated oven for 20 minutes, or until pancake is golden brown and puffed.
Sprinkle with the juice of half a lemon and dust with confectioner's sugar. Serve immediately.