Mix all ingredients and heat to melt the honey. Sift the strong bread flour in advance. Separate the egg into egg yolk and white. Preheat the oven to 355F/180C.
Put egg white in a big bowl. Whisk with a hand mixer at the highest level. When it becomes white, add sugar in 2 to 3 portions and whip up well.
Add egg yolk and mix with the lowest level on the hand mixer to smoothen out.
Add strong bread flour and mix with a rubber spatula until the flouriness is gone. Be careful not to knead.
Mix the ingredients and vegetable oil and mix well evenly from the bottom. When it is fluffy and becomes shiny, then it is OK.
Pour it in a cake pan lined with baking sheets and tap the cake pan to eliminate air pockets. Bake for 10 minutes in 355F/180C. Then reduce the temperature of the oven to 305F/150C and bake for another 20 minutes.
Prepare the cellophane wrap while baking. Spread a big sheet tightly on a cutting board.
When the castella is done, face the browned side down on the wrap and remove the cake pan. Make sure that the cellophane wrap doesn't wrinkle and center the castella in the middle.
Peel the oven sheet and wrap tightly with the cellophane wrap while the castella is still warm. This process will keep the castella moist.
Let it sit for a while with the browned side facing down. From next day onward, it's ready to eat. Cut right before eating. You can store it for about 3 days in room temperature.
Revision For the coffee flavor, it wasn't 1/2 of tablespoon but it was 1 tablespoon.
Story Behind this Recipe
This is the top selling product, which sells out quickly at our kindergarten bazaar. To make one big castella, it takes 6 eggs. But I made it to be small for a home size and used less sugar. Once you try making it, it is much more easier than you think.
Make sure to make a firm meringe! Wrap the castella while it is still steaming and letting it sit for a while makes a moist and delicious castella.
Variation: Brown sugar flavor - Change the soft light brown sugar to brown sugar. Matcha flavor - Change the strong bread flour amount to 65g + 10g of matcha. Coffee flavor - Add 1 tablespoon of instant coffee to the ingredients.