Falling down a cake rabbit hole

Sponge cake is probably my favorite baked cake (my preferred birthday cake is actually an ice cream cake). One week, a series of well-targeted Instagram reels of freshly baked sponge cakes being branded with cute logos got my wheels turning. Maybe I could make my own Pikasploot food brand iron... and then that led to the deepest cake rabbit hole I've ever been down.

What is a sponge cake?

First, some explanation – a sponge cake is broadly any cake that uses cake flour, granulated sugar, and whipped egg whites as its core base. Cake flour has a lower protein content compared to all-purpose or bread flour, which is good for cakes since we don't want gluten to form. The whipped egg whites act as a leavener, an ingredient that helps creates air pockets in the batter via chemical or physical means. Physically beating the egg whites prior to baking traps air bubbles into the batter that expands with the heat of the oven. Combined together, the egg whites and cake flour yield a light and airy crumb.

There are several different types of sponge cakes, but the ones I was mostly familiar with were chiffon cakes, Taiwanese castella cakes (Japanese castella cake is different!), and angel food cake. While gearing up to write this post, I realized I had never eaten angel food cake before, nor could I actually tell you what the difference was between the three cakes. I spent a Saturday baking all three to see what the difference was:



In fairness to angel food cake, I squished it when cutting it

In making these cakes, I learned that the main difference is what was added (or not added) on top of the core base of cake flour, whipped egg whites, and white sugar:



Chiffon cakes adds oil and egg yolk, while Taiwanese castella cake adds oil, egg yolks, butter, and milk. Angel food cake just has the base.

From this experience, I learned I didn't like angel food cake – I'm guessing it's because it doesn't have any of the added richness of egg yolks or any saturated fats. Taiwanese castella cake is baked in a water bath, which yields the most moist crumb out of all three. It also conveniently results in the flattest surface, which is perfect for applying a food brand iron.

Down the rabbit hole we go

One of the Instagram reels I saw had a recipe for castella cake, which I then tweaked to suit my tastes. For the food brand iron, I discovered an entire corner of Etsy dedicated to food brands. I found a seller who makes custom brands and sent over an SVG of the Pikasploot logo I made for this website. $70 and 2 weeks later, I was the proud owner of one adorable Pikasploot food brand:

I went a little brand crazy and used it on nearly all the cakes I made, even on some moon cakes:



I now had my food brand iron and a base castella recipe, but why stop there! I made a long list of flavors to try, and started imagining a visual grid of all the different flavors I could make. I baked cake in different form factors, and also figured out how to make them gluten free.

I ended up trying 12 flavors in addition to plain vanilla. While experimenting, I ended up using roughly 4 different methods to flavor the cake:

• Powders: I substituted 20g of the cake flour with the powder of choice. Flavors tried: Chocolate (cocoa powder), hojicha, matcha
• Cold brew tea: I soaked loose leaf tea in milk for at least a day (or 2+ days for lighter teas like jasmine), steeped the tea in the heated milk + butter/oil mixture for at least 30 minutes, and then ground up dried tea leaves to include in the batter directly. Only after doing all of that could I actually taste the tea. Flavors tried: Jasmine, English rose tea.
• Syrups: I learned if I included syrups that have any amount of acid (e.g. yuzu) directly into the milk mixture, the milk will curdle. Instead, loosening the syrup by heating it for ~10 seconds in the microwave and then incorporating it into the egg mixture afterward worked much better. Flavors tried: Honey, yuzu
• Flavoring the milk: Some flavors were more easily incorporated into the milk mixture, such as Earl grey tea bags or instant espresso. These probably work better for things meant to be drunk in liquid form originally. Flavors tried: Earl grey, coffee



When baking each flavor, I cut the recipe in half and used mini loaf pans to avoid eating a ridiculous amount of cake. To help with cake overflow, I brought cakes to work and had my coworkers try and guess the flavors; that ended up being a form of feedback as to whether I made the flavor strong enough or not. I actually have even more flavors I want to make, but my sister begged me to stop making cake so I figured this is a good enough stopping point to write about this cake adventure. If you made it this far and would like to try making castella cake yourself, see this recipe!