• 150 g (5½ oz) butter, softened
• 150 g (5½ oz) sugar, plus 2 tablespoons, extra
• 2 teaspoons vanilla extract
• 3 eggs, separated
• 250 g (9 oz/1⅔ cups) plain (all-purpose) flour
• 2 tablespoons potato flour
• 2 teaspoons baking powder
• 3 tablespoons milk
• 3 rennet apples (or other large sweet cooking apples), about 220 g (7¾ oz) each
• icing (confectioners’) sugar, for dusting

Preheat the oven to 170°C (325°F/Gas 3). Butter and flour a round 24 cm (9½ inch) springform cake tin.

Using electric beaters, whip the butter and sugar in a wide bowl until creamy. Add the vanilla, then add the egg yolks 1 at a time, whisking well after each. Whisk in the flour, potato flour and baking powder, adding the milk as the mixture thickens to make it come together in a very thick batter. Scrape the mixture off the beaters into the bowl, then wash and dry them. Use the clean beaters to whip the egg whites to snowy peaks. Using a metal spoon, fold a Scoop of the egg whites into the cake batter until evenly dispersed, then gently fold in the rest of the whites. If they are difficult to incorporate, give a quick whisk with the electric beaters to mix it all together. Scrape into the prepared tin and level the surface.

Peel, core and halve the apples. Cut across the halves into slices of 4-5 mm (⅛-¼ inch). Starting at the centre of the cake, arrange the slices slightly obliquely, pushed about halfway into the batter. Pack them tightly together, working your way outwards like the petals of a rose. It may seem like there is too much apple, but fill in any spaces as it will look lovely later. Scatter the extra 2 tablespoons of sugar evenly over the top. Bake until the apples begin to get golden and some of the edges are dark, about 45 minutes, then cover with foil and continue baking for a further 15-20 minutes or until the cake is ready. (The middle should look ever-so-faintly gooey.) It is important that the cake is not overcooked as the edges and bottom will dry out. Remove the foil and cool before removing from the tin. Serve dusted lightly with icing sugar.