This Asian sponge cake is ultra-light, soft, and bakery-perfect. Get the meringue secrets, the water bath method, pro tips, and the best flavor variations.
Prepare. Preheat the oven to 150°C (300°F). Line the bottom of an 8-inch cake pan with parchment paper, but do not grease the sides. Boil water for the water bath.
Make the egg yolk batter. In a large bowl, whisk the egg yolks lightly. Add the milk, oil (or melted butter), and vanilla, and whisk until smooth. Sift in the cake flour and gently whisk until just combined and lump-free. Set aside.
Make the meringue. In a clean, dry bowl, beat the egg whites with the cream of tartar until foamy. Gradually add the sugar in 3 batches while beating. Continue until soft to medium peaks form, where the tips curl slightly rather than standing stiff.
Fold the batter. Add one-third of the meringue to the yolk batter and gently mix to lighten it. Add the remaining meringue in two batches, folding gently with a spatula. Fold just until combined, without stirring or deflating the air.
Bake in a water bath. Pour the batter into the prepared pan and tap lightly to release large bubbles. Place the cake pan inside a larger tray and pour hot water into the tray, about 2 to 3 cm deep. Bake for 55 to 60 minutes, until the top is golden and springs back when lightly touched.
Cool. Remove from the oven and gently drop the pan from a small height to prevent shrinking. Cool the cake in the pan, or invert it on a rack, for about 30 minutes before removing. Slice with a serrated knife using a gentle sawing motion.
Notes
Use cake flour for the lightest texture, since its low protein keeps the crumb soft. If unavailable, replace 2 tbsp of all-purpose flour per cup with cornstarch.
The meringue is everything. Aim for soft to medium peaks. Over-whipped meringue causes cracks, while under-whipped causes a dense, wet cake.
Make sure the bowl and beaters are completely clean and grease-free, since any fat stops the egg whites from whipping.
Fold gently and patiently. Aggressive mixing knocks out the air that makes the cake rise and stay fluffy.
Do not open the oven during the first 40 minutes, since sudden temperature changes cause the cake to collapse.
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