You will absolutely love this ultra-soft and fluffy Taiwanese cream cheese castella cake. This is one of the softest castella sponge cakes I have ever made.
Preheat oven to 300 F (150 C) for conventional oven. If you use convection oven, lower the temperature by 20 degrees. Get the eggs out from the fridge for about 15 minutes, to let them come to room temperature
We will bake the cake in a water bath. Get another larger pan and fill it up with water, about 1 inch full and put inside the oven, on the middle rack. So the water will heat up together with the oven
Line your cake pan with parchment paper on the bottom and the sides. I used two parchment paper overlapping. So I can lift the cake out from the pan for cooling down later. If you use a loose-bottom pan, put the pan inside another pan. I found that water still manages to sip in when I double wrapping with aluminum foil
Set up a double boiler (bain marie):
Put some water in a saucepan and set a heat-proof bowl sitting on top of the saucepan. The water shouldn't be touching the bottom of the bowl
Prepare cake batter:
Add cream cheese, oil, and milk to the double boiler you set up and whisk until the cream cheese is just melted. Do not overheat. Remove from the heat and wipe the bottom of the bowl
Whisk the whole egg to loosen up. Add the yolks and whole eggs, and vanilla extract into the cheese mixture
Sift in the cake flour and salt and whisk again to combine. Set aside
Prepare egg white meringue:
Beat egg whites on low speed until foamy, then add vinegar and continue beating for another minute and then increase the speed to medium (speed 6 on KA) and add sugar in 3-4 batches and continue to beat until you get a medium-soft peak. When you lift the meringue up with a whisk, the tail will bent. Do not overwhip the meringue
Fold the meringue into the cake batter:
Add 1/3 of the meringue into the cake batter. Use a whisk to fold over to combine and when you get to the last 1/3 of meringue, switch to a spatula and swipe down and fold over to combine to make sure you scrape the bottom of the bowl to make sure the batter is folded with the meringue evenly. Work gently but fast
Pour the batter into the prepared pan. Bang the cake pan on the countertop a few times to pop large air bubbles. Place the cake pan inside the larger pan
Bake the cake:
Very carefully transfer the cake pan and put it inside the larger pan with water that you prepared earlier. Bake for the next 1 hour 50 minutes to 2 hours. Took me 2 hours with my oven. You can start checking on the cake at about 1 hour 30 minutes mark. The cake should bounce back when you gently touch it. It should be dry to touch. A cake tester should come out clean with maybe a few crumbs but it shouldn't be wet
Cooling down:
Remove from the oven and immediately and bang on the countertop a few times to minimize shrinkage. Then immediately lift the cake out from the cake pan very gently by grabbing on the parchment paper. Place on a cooling rack and gently peel off the parchment paper on the side of the cake and let it cools down completely this way before cutting. The cake will jiggle when you pat on it. It will stop jiggling once the cake has cooled down completely
To serve:
Use a serrated knife to cut the cake so you won't squish down the cotton soft cake. The castella cake can be kept at room temperature for 3 days in an air-tight container. If you are patient enough, serve it the next day and the flavor gets even better