Method
Heat the oven to 160°C/315°F/gas mark 2–3. Toss the cooking apples with the lemon juice and zest and set aside. Grease and line with baking parchment the base and sides of a 24cm (9½in) diameter springform cake tin. Beat the butter and light brown soft sugar together until light and pale. You can do this by hand, but it’s easier with an electric mixer. Add the beaten egg, a little at a time until it’s all incorporated, then trickle in the cider, stirring continuously. Sift the flours and baking powder together with the pinch of salt into a separate bowl, then fold this into the butter-and-egg mixture, followed by the chopped lemony cooking apple and the thyme leaves. Fold together to combine.
Spoon the cake batter into the prepared tin. Peel, quarter, core and thinly slice the dessert apples, and arrange the slices in a single layer around the edge of the cake. Finally, sprinkle with the demerara sugar.
Bake in the centre of the oven for 50–60 minutes or until a skewer inserted into the centre of the cake comes out clean. Transfer the cake to a wire rack to cool before serving in slices. Once cool, the unsliced cake will keep in an airtight container for 3–4 days.
