Break the eggs, separating the yolks from the whites. In a bowl, work the butter with the sugar and vanilla extract until you get a creamy consistency.
Preheat the oven to 180°C (th. 6). Incorporate the egg yolks one by one, then sift together the flour and baking powder and incorporate them.
Whip the egg whites with a pinch of salt until stiff, then gradually fold them in: first a little to loosen the mixture, then the rest with a spatula.
Peel and core the apples, cut them into cubes and add the lemon juice to prevent them from blackening. Fold them into the mixture. Butter and flour a springform pan, then pour in the mixture. Bake for 45 minutes.
Remove from the oven, sprinkle with granulated sugar and let cool for a few minutes before turning out.
