Preheat the oven to 350 degrees F (175 degrees C).

In a medium bowl, whip egg whites with an electric mixer until foamy. Sprinkle in 3 tablespoons of sugar while continuing to whip until stiff peaks form. In a separate bowl, stir together the flour, baking powder, and salt. Mix in the milk, egg yolks, and lemon juice until well blended, then fold in the egg whites using a rubber spatula or wooden spoon.

Melt the butter in a large cast-iron (or other oven-proof) skillet over medium heat. Spread the batter evenly in the pan. Layer the thinly sliced apple over the batter, and sprinkle with cinnamon and remaining sugar.