Learn how to make this Hong Kong bakery-style paper-wrapped sponge cake. Don't let their humble appearance fool you. The cake is so soft and fluffy with that traditional aroma that will remind you of your childhood.
Get the eggs out of the fridge and separate them when they are still cold. They are easier to separate when they are cold. Let the yolks and the whites come to a room temperature, this may take about 30 minutes or so
Prepare the mold and how to fold the parchment paper:
I don't have a special tall metal cup for this cake. I use paper cups that are suitable for hot drinks. The cup size is about 3.5 inches tall, 2 inches in diameter at the bottom and almost 3 inches in diameter on top
You will also need 4 pieces of parchment paper, about 8 x 6 inches each. Fold them in half and then half again. Unfold the paper and you will see the crease created by the foldings. Use a scissor to cut along the crease, leaving about 1 inch from the center
Line the cup with parchment paper. You should have no difficulty as the paper will just mold right into the cup. You just need to adjust the side slightly to make sure the paper overlaps in a decorative manner. Repeat with the rest of the cups and parchment papers. I use another cup to help me gently push the paper all in. The paper should extend about 1 to 1.5 inches above the rim of the cup because the cake will rise tall as it bakes. If it's too tall, you can trim off the paper with a scissor
Arrange the cups on top of a baking pan
Prepare the cake batter:
Preheat your oven to 350 F (180 C) for conventional oven. If you have a convection oven, preheat to 330 F (165 C). Place the oven rack 4th from the top (or adjust accordingly, you will know your oven best)
Place the egg whites in a clean mixing bowl. I use a stand mixer with a whisk attachment. You will have trouble whipping your meringue if there's a trace of grease in your utensils or bowls
In a separate bowl, whisk the egg yolks, sugar, milk, vanilla extract and oil. Sift in the cake flour and salt into the batter. Whisk to mix into a smooth batter. Set aside
Prepare the meringue:
Beat the egg whites on medium speed until frothy, add cream of tartar or lemon juice/vinegar and whip until it turns whitish and air bubbles are fine. Gradually add the sugar as you beat, in 3 batches. I beat them at medium speed (speed 6 on Kitchen Aid). This will take a bit longer compared to beating at high speed. I used to do higher speed (speed 8), but the meringue is smoother and nicer when I maintain the speed on 6 and much more stable too. I highly recommend stopping several times to check on the consistency and scraping the sides of the bowl to make sure no sugar left on the side of the bowl. Whip until you reach a stiff peak but still have a slight bent on the tip. Then lower the speed to 4 and whip for 1 minute to even out large bubbles and stop beating
Fold meringue into the batter:
Gently fold 1/3 of the meringue into the thick batter. Using a whisk, using a cutting motion and fold over to mix. Repeat this motion several rounds. Continue on with the second 1/3 of the meringue again to mix. For the last 1/3 of the meringue, use a rubber spatula instead to ensure you get all the batter at the bottom of the bowl mixed in as well. Use a cut down in the middle and fold over motion to fold gently but quickly. Make sure you don't see any more white meringue. The mixture should be fluffy and voluminous.
Pour the batter into the prepared mold. I filled them up to the rim of the cup. The cake will rise further. Use a skewer to draw a zig zag to pop bubbles inside the cake batter
Baking:
Put the baking pan in middle rack and let it bake for 25-30 minutes for the cake as tall as I make. It took mine 25 minutes. I check the cake by poking a skewer into the middle of the cake and it comes out clean. The top is dry to touch and springs back when you push it down gently. The top should be golden brown
The cake needs to be fully baked but try not to overbake. If your cake is shorter than the one I made, I would check at 20 minutes or sooner.
Cooling:
Remove the cake from the oven. I tap each mold on the counter once or twice to prevent shrinkage and then lay the cup on the side and gently wiggle the cake out from the cup. Let them cool down on the side. The cake should not collapse. They will shrink slightly, but not too much and this is normal
Serving:
If you serve them on the same day, the flavor hasn't fully developed yet. I like to let them cool down completely and then store them in air-tight container for up to 3 days. They get so much better the next day