Peel and core one medium to large apple. You only need 60 grams for the puree and 8 thin slices to decorate. Blend the apple into puree texture. You can also use an equal amount of unsweetened apple sauce
Coat the apple slices with about 1/4 tsp of cinnamon powder
Prepare the cake batter:
Preheat oven at 325 F (160 C). We will bake this cake using a water bath method if you bake it using a round pan. Get 2 pan, one 7x3 inch round pan to bake the cake and another larger pan so the 7 inch pan can sit inside. Line the bottom of the round cake pan with a parchment paper
If you are using chiffon tube pan, do not grease the pan and you don't need to line the bottom of the pan either. We won't be using a water-bath method with chiffon tube pan
Whisk to combine all the dry ingredients
Mix the yolks, oil, apple puree, sugar, and cinnamon in a mixing bowl. Whisk to combine. Sift the dry ingredients into the wet and stir to combine. It will be a bit lumpy because of the apple puree, but that's fine as long as there is no loose flour in the batter. Set aside
Make the meringue:
Make sure the mixing bowl and the whip attachment are clean and grease-free. Beat the egg whites on medium speed (speed 4 on KA) until frothy. Add the vinegar and beat again for another minute then gradually add sugar in 3 batches. Whip until the meringue reaches a stiff peak with a slight bent on the tip. You can always stop to check halfway
Fold the meringue into cake batter:
Gently fold 1/3 of the meringue into the cake batter. Using a rubber spatula or a whisk (I actually prefer to use a whisk now), swipe from the side and gently fold over to mix and then continue. Repeat this motion several rounds. Continue on with the second 1/3 of the meringue again to mix. Continue to do this until you are done with the meringue and the batter and meringue are nicely mixed
Baking in a round pan:
Pour the batter into an UNGREASED cake pan. Use a rubber spatula to smooth the surface. Gently drop the cake pan from about 10 cm height on the counter 2-3 times. This helps to pop large bubbles inside the cake batter. Very gently arrange the apple slices on top of the cake
Put the cake pan inside another larger pan. Fill the large pan with hot water, about 1 inch high. Gently transfer to the oven and bake on the middle rack for 1 hour 30 minutes. The cake should bounce back when you gently touch it. It should be dry to touch. The cake shouldn’t jiggle when you gently shake the pan. A cake tester should come out clean
Baking in a chiffon tube pan:
Pour the batter into an UNGREASED chiffon cake pan. Use a rubber spatula to smooth the surface. Gently drop the cake pan from about 10 cm height on the counter 2-3 times. This helps to pop large bubbles inside the cake batter. Very gently arrange the apple slices on top of the cake
Bake at 330 F (165 C) for 45 minutes and then 300 F (150 C) for 5-10 minute or until cake tester comes out clean.
Cooling down:
If using round pan: Take the pan out from the oven. Wipe the bottom of the pan because it's wet and drop the pan from about 10 cm height several times to minimize shrinkage. Run an offset spatula or rubber spatula around the side of the pan to loosen the cake. Invert the cake onto the cooling rack to release the cake and then flip it back. Let it cools down completely on the cooling rack before slicing
If using chiffon pan: Once out of the oven, drop the cake pan from about 10 cm height on the counter several times to prevent shrinkage. Then carefully invert the pan upside down. Please don't be tempted to remove from the pan if it's still warm. It takes about one to two hours to cool down completely
Remember to use a serrated knife and using a sawing motion to cut the cake to prevent squishing the cake