• You can read more details on ingredients, substitutions, variations, and other tips in my post that may answer your questions not covered in the recipe card
• Make sure your chiffon cake pan does not have a non-stick coating or your cake will not rise. The cake needs to cling to the side of the pan to rise tall

Bring ingredients to room temperature:

• Before you start making the recipe, make sure the eggs and milk are at room temperature. Separate the eggs when they are still cold and then let the whites and yolks come to a room temperature, about 30 minutes or so.
• If the applesauce that you use is too runny or liquidy, you need to drain off the extra liquid as this can affect the outcome of the chiffon cake
  

Very thinly slice the apple:

• You will not need the entire apple. You don't need to remove the peel. Remove the core. Cut the apple in half. Thinly slice the half apple. You can eat the other half or for other use. If you have a mandoline slicer, this helps slicing the apple thinly and consistently. You want to slice it to about 1-2 mm in thickness. Chiffon cake is very delicate so it is important to slice the apple as thin as you can

Prepare cake batter:

• Separate the egg yolks from the whites. In a separate bowl, whisk the egg yolks salt, oil, applesauce, and ground cinnamon
  
• Sift the cake flour into the yolk mixture, then use a rubber spatula to gently mix until you don't see any more loose flour.
  
• Please don't be alarmed that the batter is probably thicker than what you are used to for chiffon cake.
  

Whip the egg white meringue:

• Preheat your oven to 330 F (165 C). Place the oven rack 3rd from the top. For convection oven, lower the temperature by 20 F (15 C)
• Beat the egg whites on medium speed until frothy, add cream of tartar or lemon juice/vinegar and whip until it turns whitish and air bubbles are fine.
  
• Gradually add the sugar as you beat, in 3 batches. I beat them at medium speed (speed 4 on Kitchen Aid). This will take a bit longer than beating at high speed. I used to do higher speed (speed 6 or 8), but the meringue is smoother and nicer when I maintain the speed on 4 and much more stable too.
  
• I highly recommend stopping several times to check on the consistency and scraping the sides of the bowl to make sure no sugar left on the side of the bowl. Whip until you reach a stiff peak but still have a slight bent on the tip. Then lower the speed to 4 and whip for 1 minute to even out large bubbles and stop beating
  

Fold meringue into the cake batter:

• Gently fold in 1/3 of the meringue into the thick batter. Using a rubber spatula, swipe from the side and gently fold over to mix and then continue. Repeat this motion several rounds. Since the batter is a bit thicker, it's okay to take a bit more time to make sure the meringue and the batter really combined. You shouldn't see any streaks of egg white meringue. You can be a bit more "rough" for this first round.
  
• Continue on with the second 1/3  of the meringue again to mix. You want to be gentler now but make sure the two are well-combined. Continue to do this until you are done with the meringue and the batter and meringue are nicely mixed. You shouldn't see anymore streaks of white meringue
• Pour the cake batter into an ungreased chiffon pan. Use a chopstick or a skewer to draw a zig zag on the cake batter to pop any large air bubbles that are trapped inside and also to even out the batter. The large air bubbles will create large holes in the crumbs later. Gently drop the cake pan from about 10 cm height on the counter 2-3 times.
  
• Arrange the apple slices gently on top of the cake batter. Do not push them into the cake. Arrange only in one layer. We don't want to put too many slices as they can "weigh" down the cake
• Sprinkle with some small pearl sugar if you have some, otherwise, you can skip. Pearl sugar doesn't dissolve in baking. Do not use regular sugar or coarser sugar like turbinado sugar as they melt during baking, making the top of the cake "wet"
  

Baking:

• Pop into the oven and let it bake at 330 F (165 C) for 50 minutes or until the toothpick inserted into the middle of the cake comes out clean. The top shouldn't be wet and bounce back when you gently press on it with your finger.
• I bake this cake a bit longer than usual for 6-inch cake because I need the cake to be sturdy enough to avoid the risk of collapsing when unmoulding the chiffon cake later
• Don't be alarmed if your cake has some cracks on top because of the apple slices

Invert the cake once out of the oven:

• 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. Your chiffon pan may have the little stands for you to invert, but I find it not high enough. I use a glass jar and set the inverted pan on top of the jar and let it cool down completely. 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
  

Unmolding the cake:

• Once it has cooled down completely, use a spatula knife to run through the edge of the cake and outer middle tube to help release the cake. Gently push the base of the pan to lift the cake up. Use an offset spatula and run it between the base and the cake, pressing down to the base as you move the spatula to release the cake from the base
  
• Carefully invert the cake onto a serving plate and then flip it back up so the apple slices side is facing up again
• Usually, the bottom of the cake becomes the top of the cake with chiffon cake, but for this apple chiffon cake, the top with the apple slices is the top of the cake.
  

Serving:

• The cake actually tastes the best the next day when the flavor has time to develop. The cake feels "drier" on the same day you just bake it.
• Serve as is or with some whipped cream if you desire

To store:

• Store the cake in an airtight container at room temperature for 2-3 days if you plan to eat them within that time frame. I highly recommend serving the cake the next day as the flavor and texture get better