A twist to the traditional moist and dense carrot cake is this incredibly soft, fluffy, and spongey Taiwan-style castella carrot cake frosted with a light whipped cream cheese and walnuts.
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 a loose-bottom round cake pan. So I lined the sides and the bottom with parchment paper. If you use a loose-bottom pan, put the pan inside another pan. I found that water still manages to sip in when I just 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 the cake batter:
Add butter and milk into the bowl and heat up until butter just melted. Do not overheat. Remove from the heat and wipe the bottom of the bowl
Add yolks, vanilla, sugar, and grated carrot and whisk to combine. Sift in the cake flour, ground cinnamon,nutmeg, cloves, ginger, and salt. Whisk to combine until you don't see pockets of flour
Prepare egg white meringue:
Beat egg whites on low speed until foamy and then increase the speed to medium (speed 6 on KA) and add sugar in 3 batches and continue to beat until you get a firm peak. When you lift the meringue up with a whisk, it will hold its shape with its tail bending. 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 if you use a loose bottom cake 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. If it is, bake in a 5 minute increment and check again
Cooling down:
Remove from the oven and immediately bang the cake pan on the countertop a few times to minimize shrinkage. Then immediately lift the cake out from the cake pan very gently by grabbing the parchment paper or push it out if using a loose-bottom cake pan
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 and it may shrink down a bit and this is normal. The cake shouldn't collapse though
Prepare whipped cream cheese (only after the cake is ready to be frosted):
Put softened cream cheese, sugar, and vanilla extract in a bowl and whip until creamy. Gradually add the chilled heavy cream and whip until you get a medium-firm peak. Do not whip until it's stiff and grainy. Cover and keep this chilled in the fridge until ready to be used
Prepare the candied carrot:
Use a peeler to peel about 20 grams of carrot strips. Bring water and sugar to a simmer and then add the carrot strips and simmer for 2-3 minutes and then remove and pat dry with an absorbent paper towel
Frost the cake :
The cake should have cooled down by now. Use an offset spatula to frost the top of the cake and decorate with the candied carrot strips if using, and finely chopped walnuts. Chill the cake in the fridge for at least 2 hours until the cream is set