Preheat the oven to 350°F.
Line a baking sheet with parchment paper and place a stable baking frame (approx. 16 x 12 inches) on the sheet.
Peel the apples and cut them into small pieces. Drizzle them with lemon juice to prevent them from browning.
Separate the eggs and beat the egg whites until stiff. Set aside.
Beat the egg yolks with the sugar until frothy, then add the oil and water one after the other. Continue beating until well combined.
Mix the flour and baking powder and then sift it into the egg yolk mix. Then fold in half of the egg whites, followed by the other half.
Pour the batter into the baking frame and bake for about 15 minutes. Let the base cool afterwards.
Pour 3½ cups of apple juice into a saucepan and bring it to a boil along with the sugar.
Meanwhile, mix the pudding powder with the remaining apple juice until smooth and then add it to the boiling apple juice. Stir well.
Once the pudding starts to thicken, stir in the apple pieces.
Let the apple pudding cook for 2 minutes and then spread it evenly over the base in the baking frame.
Let the mixture cool for 1-2 hours at room temperature.
Beat the heavy cream together with the vanilla extract, cornstarch, and sugar until stiff. Finally, spread the cream over the cake and place it in the refrigerator for an hour.
Sprinkle the apple pudding cake bars with cinnamon before serving.
