Preheat the oven to 170°C. Grease the baking tin with generous amount of butter (this will create a lovely, golden and buttery crust for the cake). Set aside.
Using an electric mixer, mix the butter and sugar for couple of minutes, until pale and fluffy, then add an egg and flour and mix again to combine. The batter will be thick and sticky, don't worry, this is how it is meant to be.
Spoon roughly about ⅔ of the cake batter into the greased baking tin and use a fork or small offset spatula to spread it lightly over the base of the baking tin. Make sure the batter covers the base of the tin completely.
Slice peeled and cored apples into 1cm slices, then place them into a large bowl and toss together with 3 tablespoon of soft light brown or demerara sugar and cinnamon. Arrange the apples in a thick layer on top of the cake mixture in the baking tin. Scatter small dollops of apricot jam on top of the apples and spread it roughly.
Spoon over the remaining cake batter on top, and spread it over the apples, using fork or small spatula. Don't worry if few gaps remain here and there, you don't have to cover it perfectly, just more or less (the batter will spread as it bakes). Sprinkle the cake with 1 tablespoon of demerara sugar and bake for 1 hour or until toothpick inserted in the middle comes out clean and the apples are tender.
Remove from the oven and allow to cool for 10 minutes, before removing the cake from the tin. Serve this cake warm or cold, dusted with icing sugar and some clotted cream or a scoop of vanilla ice cream, if you would like.
Self-raising flour can be replace by plain, all-purpose flour. For this recipe, use 200g of plain flour mixed with 1 teaspoon of baking powder and 1 teaspoon baking soda.
Use and ice cream scoop or cookie scoop if you have one to divide and spoon out the cake batter.
Make sure to use all of the apples. There should be nice, thick layer of them on top.
Store any leftovers of this cake in the airtight container at room temperature for up to 3 days.
To freeze, wrap the whole cake or individual slices into double layer of clingfilm or reusable kitchen wrap and place in the freezer friendly bag. Freeze for up to 3 months. Thaw overnight in the fridge and bring to room temperature before serving.