Preheat the oven to 325°F (170°C) with a rack in the center.
Make the milk tea mixture.
In a small saucepan, heat the milk and add the tea. Allow the milk to simmer, then remove from the heat and allow the tea to steep, for at least 15 minutes.
Make the yolk batter.
Heat the oil in a saucepan over medium heat, until it reaches about 176°F (80°C). Remove from heat. Add the cake flour and whisk until combined. Transfer the mixture to a large bowl, cover, and cool for a few minutes.
Mix in the strained milk tea. Add the yolks, baking powder, miso, and sugar and whisk until combined and smooth. Set aside.
Make the firm peaks meringue.
In a stand mixer fitted with the whisk attachment, beat the egg whites until foamy, then add the cream of tartar.
Beat for another minute, until whiter, then gradually add the sugar. Beat until the firm peaks form. (When you flip the whisk upside down, the peak, while more distinct than soft peaks, will still droop and curl back on itself, like a defined bird’s beak.)
Make the final batter.
Add one-fourth of the meringue to the yolk batter. Gently whisk until incorporated. Add another fourth of the meringue to the yolk batter and whisk until incorporated. Then pour all the batter into the bowl with the remaining meringue. Use a flexible spatula to gently fold the meringue into the batter, until homogenous, thick, and creamy. There should be no white streaks remaining in the batter. If stubborn lumps of meringue remain, use a whisk to gently mix the final batter. Don’t over-mix.
Transfer the batter evenly into the lined cups. The cups should be about 3/4 full. Bake for about 20 minutes, until the tops are golden brown. These cakes should not crack, but some cracks are OK.
Remove from the oven and cool on a wire rack, though they are best enjoyed hot or warm. Store leftover spongecakes in airtight containers for up to two days at room temperature. Feel free to reheat the spongecakes in the microwave. Happy Lunar New Year!
Note:
For this recipe, you’d want to use a deep muffin tin or individual tumbler popover tins lined with tulip cupcake liners (or parchment paper that popovers or stands tall in the tin so the sponge cakes can rise nicely). You should have enough batter to make about 6 tall spongecakes. PS: Be sure to separate your eggs first!