Castella Cake London: A Baker's Guide to the Japanese Sponge

Castella cake, or Kasutera, is a Japanese sponge cake with Portuguese roots, known for its dense, moist crumb and subtle honey sweetness. This recipe creates a beautifully golden, tender loaf that’s surprisingly simple to make at home in London, where Japanese ingredients are readily available but the cake itself is a treat worth mastering. The key to its signature texture lies in the technique: a hot milk-butter mixture and a long, gentle bake that produces a fine, even crumb.

Ingredients

6 large eggs (about 300 g / 10.5 oz), at room temperature
180 g (3/4 cup + 2 tbsp) granulated sugar
180 g (1 1/2 cups) bread flour, sifted
40 g (3 tbsp) honey
40 g (3 tbsp) whole milk
40 g (3 tbsp) unsalted butter
1/4 tsp salt

Instructions

Preheat your oven to 320°F (160°C). Line a 9×5-inch (23×13 cm) loaf pan with parchment paper, leaving some overhang on the long sides for easy lifting.
In a small saucepan, combine the milk, butter, and honey. Heat over low, stirring occasionally, until the butter is melted and the mixture is warm (not boiling). Remove from heat and set aside.
In a large mixing bowl, beat the eggs and sugar together using an electric mixer on high speed. Beat for about 8-10 minutes, until the mixture is pale, thick, and has tripled in volume. When you lift the beaters, the batter should fall in a thick ribbon that holds its shape on the surface for a few seconds.
Reduce the mixer speed to low and slowly pour in the warm milk-butter-honey mixture. Mix just until combined.
Sift the bread flour and salt into the batter in three additions, folding gently with a spatula after each addition. Fold until no streaks of flour remain, being careful not to deflate the batter.
Pour the batter into the prepared pan. Tap the pan firmly on the counter a few times to release any large air bubbles.
Bake for 55-65 minutes, or until the top is deep golden brown and a skewer inserted into the center comes out clean. The cake will rise and may crack slightly on top, which is normal.
Remove from the oven and immediately cover the pan with plastic wrap. This traps steam and helps keep the cake moist. Let it cool completely in the pan, about 1 hour.
Once cool, lift the cake out using the parchment overhang. Wrap it tightly in plastic wrap and refrigerate for at least 4 hours, or overnight, before slicing. This step is crucial for achieving the dense, moist texture.

Tips

Use bread flour: Bread flour has more protein than all-purpose, which gives the cake its characteristic chewy, dense crumb. If you only have all-purpose, you can use it, but the texture will be slightly softer.
Don’t skip the chill: Refrigerating the baked cake overnight allows the moisture to redistribute and the crumb to set, making it much easier to slice cleanly and giving it the proper texture.
Beat the eggs well: The egg foam is the only leavening agent. Under-beating will result in a flat, dense cake. The ribbon stage is non-negotiable.
Wrap while warm: Covering the hot cake with plastic wrap as soon as it comes out of the oven creates a moist environment that prevents the top from drying out.

Serving Suggestions

Castella is delicious on its own, but it shines when paired with a cup of green tea or coffee. In Japan, it’s often served as a tea-time snack or a light dessert. You can also serve it with a dollop of whipped cream and fresh berries, or lightly toasted and spread with butter. For a more indulgent treat, drizzle with a little honey or sweetened condensed milk.

Variations

Matcha Castella: Replace 1 tablespoon of the bread flour with 1 tablespoon of matcha powder. Sift it together with the flour before adding.
Chocolate Castella: Replace 20 g (about 2 1/2 tbsp) of the bread flour with unsweetened cocoa powder.
Brown Sugar Castella: Substitute the granulated sugar with light brown sugar for a deeper, caramel-like flavor.

Storage and Reheating

Store the castella cake in an airtight container or wrapped tightly in plastic wrap in the refrigerator for up to 5 days. The cake actually improves in flavor and texture after a day or two. To freeze, wrap the whole cake or individual slices tightly in plastic wrap and then foil. Freeze for up to 3 months. Thaw overnight in the refrigerator before serving. To reheat, place a slice on a plate and microwave for 10-15 seconds, or toast lightly in a toaster oven until warm.

Frequently Asked Questions

Why did my castella cake sink in the middle? This usually happens if the batter was over-mixed after adding the flour, which deflates the air bubbles. It can also happen if the oven temperature is too low or the cake is underbaked. Make sure to fold gently and check your oven temperature with an oven thermometer.

Can I use all-purpose flour instead of bread flour? Yes, you can, but the texture will be less dense and chewy, and more like a regular sponge cake. The bread flour is what gives castella its signature tight crumb.

Why is my cake too dry? Overbaking is the most common cause. Start checking for doneness at 55 minutes. Also, ensure you cover the cake with plastic wrap immediately after baking to trap steam. The chilling step also helps retain moisture.

Can I make this without a stand mixer? Yes, a hand mixer will work, but you’ll need to beat the eggs for longer, possibly 12-15 minutes, to reach the ribbon stage. Be patient and don’t rush it.

How do I get clean slices? Use a serrated knife and slice the cake while it’s cold, straight from the refrigerator. Wipe the knife with a damp cloth between cuts for the cleanest edges.

Is this cake supposed to be very sweet? Traditional castella is moderately sweet. The honey adds a subtle floral note. If you prefer a less sweet cake, you can reduce the sugar to 150 g (3/4 cup), but the texture may be slightly affected.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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Castella Cake London: A Baker’s Guide to the Japanese Sponge