Preheat the oven to 350°F / 180°C. Butter and flour a 9in / 23cm springform pan.
Beat 125g of softened butter, 115g of sugar, and 1 pinch of salt for 3-5 minutes, until pale and creamy. Add 1 teaspoon of vanilla extract and the zest and juice of 1 lemon.
Separate 4 eggs. Beat the yolks into the butter mixture. In a clean bowl, whisk the whites with 60g of sugar for the meringue until stiff.
Mix 220g of all-purpose flour, ½ teaspoon of baking powder, and 40g of cornstarch. Stir into the butter mixture with 100ml of milk.
Stir in a spoonful of the whites, then gently fold in the rest. Spread in the pan.
Press 800g of cored apple wedges into the batter. Bake for 45-50 minutes, until golden and a skewer inserted into the center comes out clean.
Cool completely before removing from the pan. Dust with 2 teaspoons of icing sugar.
