How To Make Castella Cake (Japanese Sponge Cake Recipe)

Gather the ingredients together and preheat the oven to 375 degrees Fahrenheit. \n Prepare the loaf pan by lining it with parchment paper.

Over medium heat, simmer the mirin in a small pot until it's reduced to half its original volume. When it cools down, it will have a syrupy consistency.\n Tip: If you reduce the mirin too much, it may solidify like candy when it cools. If this happens, don't worry; simply add a little water and reheat it.

In a large bowl, use a hand mixer or stand mixer to combine egg yolks and 50 grams of sugar until the mixture thickens. Once it's thick, introduce the cooled, reduced mirin and a few drops of soy sauce, and mix thoroughly. Gradually incorporate olive oil, ensuring a well-mixed cake batter.

In a separate medium-sized bowl, combine the egg whites with 1 tablespoon of the remaining sugar using a hand mixer or a stand mixer. Gradually add the rest of the sugar to the egg whites in 2-3 portions, beating until stiff peaks form.

Start by adding ⅓ of the egg white mixture to the yolk mixture and thoroughly combine them. Then, incorporate the sifted flour and mix until fully blended. Finally, gently fold in the remaining egg white mixture in 2-3 portions, taking care not to overmix.

Pour the batter into the loaf pan, giving it a gentle tap to eliminate any air bubbles. Use a chopstick to create a zigzag pattern in the batter (a useful tip for removing air bubbles). \n Bake for 40-45 minutes, positioning a bowl of lukewarm water beside it. To check if the Castella is done, insert a toothpick or paring knife into the center; when it comes out clean, your Castella is ready to enjoy.\n Tip: The bowl of warm water remains beside the cake in the oven to help keep the cake moist. Without this, the cake may become too dry.

Once you remove the cake from the oven, gently tap the loaf pan twice from a distance of about 4 inches to prevent the cake from shrinking.\n Grease a piece of plastic wrap or parchment paper with oil, place it on the cake's surface, and then flip the cake onto it to remove the loaf pan. Allow the cake to cool completely.\n Once the cake is cool, cover it with plastic wrap and let it rest at room temperature for a minimum of 6 hours, or overnight.\n Tip: Freshly baked Castella is quite hot, and its texture and flavor have yet to fully settle. Allowing it to cool down and rest for a while is essential as it helps evenly distribute moisture and flavors inside, ultimately enhancing its deliciousness.

After allowing the Castella cake to rest for over 6 hours, carefully remove the plastic wrap and parchment paper. Use a bread knife to trim the cake's edges, and then slice it to your preferred thickness. Now, it's ready to enjoy!\n Tip: For clean and beautiful slices, moisten the bread knife before each cut.