Wash, peel, and dice the apples. Place them in a skillet with a little oil and cook for 10 minutes.

Let the apples cool slightly. Meanwhile, separate the eggs, placing the yolks and whites in separate bowls. Beat the egg whites until stiff peaks form. In another bowl, whisk the yolks and add the sugar, flour, milk, and cinnamon. Mix well, then gently fold in the beaten egg whites.

Cook the mixture in a skillet with a lid for 5 minutes. Flip the frittata and cook for another 5 minutes. You can also bake it in the oven if you prefer.

Let it cool, then sprinkle with powdered sugar.