Ultimate Jiggly Taiwanese Castella Cake

1.Prepare the Pan and Oven: Preheat your oven to 150°C (300°F). Line an 8-inch square baking pan with parchment paper, ensuring the paper extends up the sides to create a collar, which helps the cake rise evenly. Place the prepared pan inside a larger roasting pan (this will be used for the water bath).

2.Make the Milk/Butter Base: In a small saucepan, combine the milk and butter. Heat gently over low heat, stirring occasionally, until the butter is completely melted and the mixture is warm (do not boil). Remove from heat.

3.Incorporate Dry Ingredients: Sift the cake flour and cornstarch directly into the warm milk/butter mixture. Whisk vigorously until the mixture is completely smooth and glossy, resembling a thick paste or pastry cream. Set aside to cool slightly.

4.Prepare the Yolks: In a separate medium bowl, whisk the 6 egg yolks and 2 whole eggs together until just combined. Whisk in 20g of the granulated sugar and the salt until the mixture is uniform in color.

5.Combine Bases: Gently whisk the slightly cooled milk/butter paste into the egg yolk mixture until fully incorporated and smooth. Strain this batter through a fine-mesh sieve into a clean bowl to ensure no lumps remain.

6.Make the Meringue: In a very clean, grease-free bowl, beat the egg whites on medium speed until foamy. Add the lemon juice or vinegar. Gradually add the remaining 60g of sugar in three additions, beating until stiff, glossy peaks form. The meringue should hold its shape firmly when the whisk is lifted.

7.Fold the Batter: Take about one-third of the meringue and gently fold it into the yolk batter to lighten it. Then, gently fold the lightened batter into the remaining meringue in two additions, using a spatula to cut down the middle and sweep up the sides. Be careful not to deflate the air; stop folding just when no white streaks remain.

8.Bake with Water Bath: Pour the final batter into the prepared square pan. Gently tap the pan a few times on the counter to release any large air bubbles. Place the pan inside the larger roasting pan. Carefully pour hot water into the roasting pan until it reaches about 1 inch up the side of the cake pan (water bath).

9.Bake and Cool: Bake at 150°C (300°F) for 60 to 75 minutes. The cake is done when it is golden brown on top and springs back lightly when touched. If the top browns too quickly, loosely cover it with foil after 45 minutes.

10.Rest and Unmold: Remove the cake from the oven and immediately remove it from the water bath. Let it cool in the pan on a wire rack for about 15 minutes. Run a thin offset spatula or knife around the edges to loosen it. Invert the cake onto a cooling rack, peel off the parchment paper, and let it cool completely upside down for another 30 minutes to help it settle and achieve the perfect jiggly texture. Slice and serve.