Using the whisk on a hand mixer, beat the sugar, egg yolks and water in a bowl for approx. 5 mins. until the mixture is light and fluffy. Beat the egg whites with the salt until stiff, add the sugar, continue beating until the egg whites turn glossy. Mix the flour, baking powder and almonds, add to the mixture in layers along with the egg whites and apple, carefully fold in using a rubber spatula, transfer to the prepared tin.
Approx. 45 mins. in the lower half of an oven preheated to 180°C, cover the sponge with foil towards the end of the baking time if necessary. Remove from the oven, allow to cool slightly, remove the tin frame, tip the sponge out onto a cooling rack, remove the baking paper and leave to cool completely. Cut twice through the sponge.
Mix the blueberries, sugar and water in a pan, simmer for approx. 5 mins., puree, press through a sieve, leave to cool.
Pour the apple juice into a wide pan, bring to the boil along with the sugar and lemon juice. Add the apples, cover and simmer for approx. 5 mins. until just soft. Remove the pan from the heat, leave the apples to cool in the liquid.
Cream cheese mixture
Place the butter in a bowl and stir in the cream cheese and icing sugar. Halve the mixture, transfer one half to a piping bag without a nozzle, chill. Halve the remaining mixture. Mix one half with ½ tbsp of blueberry compote and the other half with 3 tbsp of blueberry compote. Transfer each mixture separately to a piping bag without a nozzle, chill for approx. 1 hr.
Place the sponge base on a cake plate. Drizzle all three cut surfaces with the remainder of the blueberry compote and the apple liquid. Arrange half of the apple slices on the base, place the second sponge on top. Add the remaining apple slices, place the third sponge on top. Spread the plain cream cheese mixture over the top of the cake and around the upper third. Spread the coloured cream cheese mixtures over the lower two thirds, smooth down all the way around. Cover the cake and chill in the fridge for approx. 30 mins.