3 medium apples
1/2 medium lemon
4 tbsp granulated sugar
150g unsalted butter,
1/2 teaspoon vanilla extract
3 large eggs
200g all-purpose flour
2 teaspoons baking powder
1/4 teaspoon fine salt
2 tablespoons demerara sugar
Pre-heat the oven to 180°C. Line the bottom of a 20cm springform pan with parchment paper; set aside.
Peel, core, and quarter the apples. Thinly slice each quarter lengthwise without cutting all the way through to the core side, leaving the quarter hinged together like a fan. Finely grate the zest of the lemon into a bowl. Squeeze the juice from the lemon half into a small bowl; set aside.
Add the sugar and butter to the lemon zest and beat on medium speed until light and fluffy. Add the vanilla and 1 of the eggs. Beat until combined before adding the second egg. Beat until combined and then add the third egg. Scrape down the sides of the bowl again and beat until combined.
Whisk together the flour, baking powder, and salt together in a medium bowl. With the mixer on low speed, beat in the flour mixture until just combined, and beat in the reserved lemon juice. Scrape down the sides with a spatula and give the batter one last mix by hand.
Scrape the batter into the prepared pan and smooth the top. Gently press the apple quarters into the batter, core-side down, leaving only a bit of space between each quarter. If you have any apple left over, separate the slices and insert them into any open space available. Sprinkle the top evenly with the demerara sugar.
Bake for 20 minutes. Rotate the pan and continue baking until the cake is golden-brown and a tester inserted into the cake (not apple) comes out clean, 15 to 20 minutes more.
Place the pan on a wire rack to cool for 5 minutes. Run a thin knife around the edge of the cake and removing the springform ring. Let cool to room temperature.