Name: Fluffy Castella Cake
Prep time: 25 min
Cook time: 1 h
Total time: 1 h 25 min
Ingredients: 6 large eggs, separated; 3/4 cup plus 2 tbsp (100 g) cake flour (or all-purpose flour); 7 tbsp (100 g) unsalted butter (or scant 1/2 cup / 100 ml vegetable oil); 1/3 cup plus 1 tbsp (100 g) milk; 1/2 cup (100 g) sugar; 1 tbsp plus 1 tsp (10 g) cornstarch (optional); 1 tsp (5 g) lemon juice (optional); 1 tsp vanilla extract (optional); pinch (1 g) salt (optional)

Castella is a sponge cake built on equal weights of four pantry staples (flour, butter, milk, and sugar) with six eggs doing the lifting that baking powder usually handles. There are no chemical leaveners in the ingredient list because none are needed when you manage the foam correctly.

The hot roux step and soft-peak egg whites are the two things that separate a tight, dry crumb from the pale, bouncy slice this cake is known for. A low 300°F oven and a water bath handle the rest.

Slices cut clean at room temperature and get a little denser and fudgier after a night in the fridge, which is how I usually prefer them.

Serve with green tea or plain black coffee. Both cut through the rich egg flavor without overpowering it.

Prep: 25 minutes · Cook: 60 minutes · Total: about 2 hours (with cooling) · Serves: 8

Why does my castella cake crack on top? Cracking happens when the oven heat is too high or the egg whites are beaten too stiff.

The trapped air expands rapidly and bursts right through the fragile crust. You can prevent this by whipping the whites only to soft peaks.

A water bath also moderates the baking temperature.

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Grab These Ingredients

6 large eggs, separated
3/4 cup plus 2 tbsp (100 g) cake flour (or all-purpose flour)
7 tbsp (100 g) unsalted butter (or scant 1/2 cup / 100 ml vegetable oil)
1/3 cup plus 1 tbsp (100 g) milk
1/2 cup (100 g) sugar
1 tbsp plus 1 tsp (10 g) cornstarch (optional)
1 tsp (5 g) lemon juice (optional)
1 tsp vanilla extract (optional)
pinch (1 g) salt (optional)

Ingredient Notes and Swaps

Weighing your main components is absolutely critical here. The classic Emojoie recipe scales consistently if you keep the equal ratios, offering a 65-gram version or a 35-gram version for every main ingredient.

Using a digital scale removes the variation you get with volume cups. US cup conversions are listed above, but gram measurements are more reliable for this cake.

Emojoie specifies 6 egg yolks and 6 egg whites for the 100-gram ratio. I use six large eggs, making sure to separate the yolks from the whites while they’re cold.

Cold eggs separate cleanly, but the whites whip up much better once they reach room temperature.

Cake flour gives the softest possible crumb because of its lower protein content. You can certainly substitute all-purpose flour if that’s what you have on hand.

The texture will be slightly less bouncy, but the flavor remains wonderful.

Let’s Make It

Prepare the pan. Line a 7-inch (18 cm) square pan with parchment paper, per the Emojoie recipe for the 100-gram ratio. Leave an overhang on the sides so you can lift the cake out once the edges pull away from the paper.
Heat the liquids. Warm the butter and milk together in a small saucepan over low heat. You want the mixture just hot enough to melt the butter completely, but stop before it reaches a rolling boil.
Mix the roux. Pour the hot liquid directly into your weighed flour and whisk them together. The heat cooks the starches slightly to form a smooth paste that looks thick and pulls away from the sides of the bowl.
Incorporate the yolks. Whisk the egg yolks and vanilla extract into the warm flour paste one at a time. Continue mixing until the batter becomes entirely smooth and falls off the whisk in a thick ribbon.
Whip the whites. Beat the egg whites with the lemon juice and salt until foamy, then gradually add the sugar. Stop when you reach soft peaks that flop over slightly, since stiff peaks will cause the crust to crack in the oven.
Fold the batter. Gently fold the whipped egg whites into the yolk mixture in three separate additions. Scrape the bottom of the bowl carefully until no white streaks remain and the batter looks uniform and fluffy.
Bake in a water bath. Place your cake pan inside a larger roasting pan. Pour warm to hot water (not boiling) halfway up the sides of the outer pan, as Yummy Treats recommends. Bake at 300°F (150°C) until the top springs back to a light touch, about 60 minutes.
Cool the cake. The recipes omit cooling instructions entirely, so I remove the pan from the water bath and let it sit on a wire rack. Wait until it feels completely cool to the touch before lifting it out by the parchment.

Storing and Reheating

Wrap any remaining castella cake very tightly in plastic wrap once it cools completely. This delicate sponge dries out rapidly if exposed to the ambient air.

You can keep it at room temperature for the first day, but the high egg content means it really belongs in the refrigerator after that. Chilled slices actually develop a slightly denser, wonderfully fudgy texture that many people prefer.

You can eat them cold straight from the fridge or let them sit on the counter for twenty minutes to soften up. For longer storage, wrap individual portions in plastic wrap and place them in a heavy freezer bag.

They freeze beautifully for up to a month. Thaw a slice overnight in the refrigerator whenever you need a quick dessert for a packed lunch.

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