• The recipe can be used with 7 or 8-inch chiffon tube pan. The former is recommended if you do a slit-top method. It yields a really tall cake. The 8-inch yield a shorter cake with or without the slit-top method.
• 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
• I strongly suggest weighing the ingredients including the egg yolks and the whites because the size of the eggs may vary. If the eggs are off by a few grams, it's not really a big deal
• Get the eggs out of the fridge and separate them when they are still cold. They are easier to separate when they are cold. Let the yolks and the whites come to a room temperature, this may take about 30 minutes or so
• If you choose to do slit-top version: start preheating the oven at 385 F (195 C) for conventional oven. For convection oven,lower the temperature by 20 F (15 C). Position the rack to the lower 3rd of the oven
• If you choose to do regular bake without the slit: start preheating the oven at 330 F (165 C) for conventional oven. For convection oven,lower the temperature by 20 F (15 C). Position the rack to the lower 3rd of the oven

Prepare the cake batter:

• Combine whole wheat flour, cornstarch, baking powder, salt, and cornstarch in a mixing bowl and set aside
• Whisk the egg yolks, brown sugar, oil, and milk until they emulsify (combined nicely). Add the flour mixture into the yolk batter and whisk until combined. Set aside

Prepare the meringue:

• Beat the egg whites on medium speed until frothy
• Add lemon juice/vinegar and whip until it turns whitish and air bubbles are fine.
• Gradually add brown sugar as you beat, in 3 batches. I beat them at medium speed (speed 6 on Kitchen Aid). This will take a bit longer compared to beating at high speed. I used to do higher speed (speed 8), but the meringue is smoother and nicer when I maintain the speed on 6 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 the meringue into the cake batter:

• Gently fold 1/3 of the meringue into the thick batter. Using a whisk, using a cutting motion and fold over to mix. Repeat this motion several rounds. Continue on with the second 1/3  of the meringue again to mix.
• For the last 1/3 of the meringue, use a rubber spatula instead to ensure you get all the batter at the bottom of the bowl mixed in as well. Use a cut down in the middle
• Then fold-over motion to fold gently but quickly. Make sure you don't see any more white meringue.
• The mixture should be fluffy and voluminous.
• Pour the batter into an UNGREASED chiffon cake 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.

Bake (If you choose to do the slit-top version):

• Bake at 385 F (195 C) for 13–14 minutes, then quickly remove the cake from the oven and slit the top lengthwise, about 1/2-inch deep, with a sharp knife (this helps it rise evenly following the slit lines). Wipe the knife after each slit. Try to complete this in less than 1 minute.
• Return to the oven, reduce the heat to 330 F (165C), and bake for another 45 minutes for 8-inch cake and 50 minutes for 7-inch cake, or until the top is dry to the touch and springs back slightly when pressed. For convection oven,lower the temperature by 20 F (15 C)

Bake (without the slit-top):

• Put the chiffon pan in the middle rack and let it bake for 45-50 minutes for 8-inch cake, 50-55 minutes for 7-inch cake. The time is just for reference. Your oven may need less or more time to bake.

Cool:

• Immediately invert the pan upside down and cool completely before unmolding.

Unmolding:

• Run a thin knife around the edges and the center of the tube to release the cake. Then run a knife underneath the base. Carefully unmold the chiffon cake. For the slit-top chiffon cake, the cake can be placed upside down like usual, or with the slit top on top