Preheat the oven to 180ºC. Grease and line a 20 cm square baking tin with parchment paper, extending the paper over the sides to form handles.Cream the butter and castor sugar together until light. Add the egg yolk and beat again to combine.Sift together the flour, salt and baking powder. Add the flour to the butter mixture and combine to form a soft dough.Press the dough into the base of the baking tin and smooth over with the back of a spoon. Bake for about 30 minutes until golden and cooked through. Set aside to cool.To make the apple filling, place the apples and water in a wide based pan. Simmer for about 15 minutes until soft with no water remaining. Add the butter and sugar, turn up the heat and cook until the apples are slightly caramelised.Set aside to cool before spreading over the shortbread biscuit base.For the caramel, place the sugar in a heavy based saucepan on a medium-high heat. Do not stir. Swirl the pan from time to time until all the sugar has melted and is a deep caramel colour. Add the butter and then the cream. Allow to bubble away until the caramel is smooth and glossy.Pour the hot caramel over the apples and smooth over. Place the baking tin in the fridge until the caramel is set and cool.Finally, make the ganache by gently melting together the chocolate and cream. Whisk until completely smooth. Pour the ganache over the apples and spread with an off-set spatula to cover the caramel. Scatter with sea salt flakes. Chill until the chocolate sets completely.Remove the entire bake from the tin by lifting the extended paper handles. Cut into bars or squares. Store covered in the fridge.Reprinted with the permission of Bibbyskitchen@36. To see more click here.To receive quick and convenient weekday recipes, join our Easy Weekday Meals mailing list, and for up-to-date trending food, restaurant and wine news subscribe to our Editor’s Weekly newsletter.