Preheat the oven to 400°F (200°C). Peel and core the apple, then slice it into thick rings, about 1/2 inch (1 cm) thick. Separate the egg white from the yolk. In a clean bowl, beat the egg white with a pinch of salt until stiff peaks form. In another bowl, whisk the egg yolk with the Greek yogurt and flour (or cornstarch), then gently fold in the beaten egg white. If you like, add a little ground cinnamon or vanilla powder.

Five minutes before the end of baking, flip the fritters over. Enjoy!