Step 1

Preheat and prepare:Preheat the oven to 300°F and line an 8 by 8 by 3 inch pan with parchment paper. Also prepare some hot water and a larger oven safe tray/pan for the water bath.

Step 2

Make the base batter:In a large mixing bowl, sift in the cake flour to remove any lumps. Add the oil and melted butter and whisk until smooth. Add the milk and mix until just combined and the batter looks smooth. Add the egg yolks and vanilla and mix until well combined. Set aside.

Step 3

Make the meringue:Place the egg whites with the vinegar in another large mixing bowl. Using a hand mixer, beat the egg whites on medium high speed until foamy. Add the sugar in increments while continuing to mix on medium high speed until all the sugar has been added.

Step 4

Reduce the speed to medium and continue to beat the meringue until medium peak. You'll know it's medium peak when you lift the mixer and the meringue forms a peak with a slight hook. *Please refer to the post for photo reference!*

Step 5

Incorporate the meringue:Place a third of the meringue into the prepared batter base. Gently fold with a spatula with a "J" motion to incorporate the meringue. Repeat two more times with the remaining meringue. On the last mix, make sure to fold until the meringue is completely incorporated and the batter is uniform in color. Make sure to also scrape the bottom and sides of the bowl!

Step 6

Bake the Taiwanese castella cake:Pour the batter into the prepared cake pan and gently shake to level it out. Give the pan a firm tap on the counter to pop any large air bubbles.

Step 7

Place the square cake pan in the larger pan or tray and place it in the oven. Pour hot water into the outer pan, about a quarter to half way up the sides of the square pan.

Step 8

Bake the castella cake for about 70 minutes, or until the cake is golden brown on top and a toothpick inserted in the middle comes out clean. Remove the cake from the oven.*If the surface of the cake is not as golden brown as you'd like, broil for about 30 seconds.*

Step 9

Cut and serve:Let the the Tawainese castella cake cool for a moment then remove it from the cake pan by lifting. Peel the parchment paper from the cake and slice the cake into 8 equal pieces, or to your preferred size.

Step 10

The cake is jiggliest while it's hot, but it will taste quite eggy. As it cools, the cake will deflate slightly, becoming less jiggly. Once it's comepletely cooled or chilled, the cake will taste much better. It's great on its own or with some whipped cream and fruits.