Castella Cake (Japanese Honey Sponge)

Before you start

Castella is a rectangular sponge cake associated with Nagasaki and descended from cakes brought to Japan by Portuguese traders. It has no butter and no chemical leavening. The structure comes entirely from whole eggs whipped with sugar and honey into a thick, stable foam, then bound with bread flour, which gives the crumb its characteristic springy, slightly chewy bite.

Warming the eggs before whipping helps the foam reach full volume, and gentle folding keeps it intact. Bake at a low temperature for a long time, then wrap the warm cake in plastic and leave it overnight. That rest sounds optional but matters: moisture from the crumb moves to the top and sides, making the whole loaf evenly moist and the honey flavor fuller.

Ingredients

• 4 large (about 200 g without shells) eggs — room temperature
• 100 g (½ cup) granulated sugar
• 40 g (2 tbsp) honey — plus 1 tsp mixed with 1 tsp hot water for glazing
• 30 ml (2 tbsp) whole milk — warm
• 100 g (¾ cup plus 1 tbsp) bread flour — sifted twice
• 1 tbsp granulated sugar or zarame (coarse sugar) — optional, for the base

Method

1. Heat the oven to 160°C (320°F) with a rack in the lower third. Line the loaf pan with parchment that rises 3 cm above the rim. Sprinkle the coarse sugar over the base, if using.
2. Stir the honey into the warm milk until dissolved. Sift the bread flour twice and set it aside.
3. Whisk the eggs and sugar in the mixer bowl. Set the bowl over a pan of barely simmering water and whisk constantly until the mixture is warm to the touch, about 40°C (104°F), and the sugar has dissolved.
4. Move the bowl to the mixer and whip on high for 6 to 8 minutes, until pale, nearly tripled and thick enough that a ribbon dropped from the whisk stays on the surface for several seconds. Lower to medium-low for 2 minutes to make the bubbles smaller and more even.
5. Pour the honey-milk down the side of the bowl and mix on low for 10 seconds. Sift the flour over in three additions, folding with a large balloon whisk or spatula until no dry spots remain. Fold gently but thoroughly; the batter should be thick, glossy and fall in ribbons.
6. Pour the batter into the pan from a low height. Run a skewer through it in a zigzag to pop large bubbles, then tap the pan once on the counter.
7. Bake for 10 minutes at 160°C (320°F), then lower the oven to 150°C (300°F) and bake for 35 to 45 minutes more, until the top is deep brown and a skewer comes out clean. The cake should spring back firmly when pressed.
8. Brush the hot top with the honey glaze. Lift the cake from the pan, peel off the side paper, and while it is still warm wrap it tightly in plastic. Invert it onto a board, top side down, and rest at room temperature for at least 6 hours.
9. Unwrap, trim the sides with a sharp serrated knife to show the brown top and bottom against the yellow crumb, and cut into 2.5 cm (1 in) slices.

Tips for success

• If the top browns too quickly, lay a sheet of foil over it for the last 15 minutes.
• Fold in a figure-eight, cutting through the center and lifting from the bottom, to blend flour without deflating the foam.
• Wrapping the cake while warm feels wrong, but the trapped steam is what keeps the crumb moist and the top sticky.

Substitutions

Bread flour

All-purpose flour gives a softer, more tender crumb with less of the characteristic springy bite.

Honey

Use the same amount of mizuame (rice syrup) for a milder, glossier cake. Maple syrup gives a different but pleasant flavor.

Loaf pan

An 18 cm (7 in) square pan works; the cake is shallower, so start checking at 30 minutes after the temperature drop.

Variations

Matcha castella

Replace 8 g of the bread flour with matcha powder, sifting them together, and skip the honey glaze.

Brown sugar castella

Replace half the granulated sugar with dark brown sugar for a deeper, faintly molasses flavor and a darker crumb. Keep the honey as written.

Troubleshooting

Cake shrank and wrinkled after baking

It was underbaked or the foam was underwhipped. Whip until a ribbon holds for several seconds and bake until a skewer is clean and the top springs back.

Dense, wet layer at the bottom

Flour sank because it was not folded in fully, or the foam deflated. Sift the flour twice and fold until completely smooth.

Large holes in the crumb

Air bubbles were left in the batter. Mix on low for a couple of minutes after whipping and run a skewer through the batter in the pan.

Storage

Keep the cake wrapped in plastic at room temperature for up to 4 days; it gets more evenly moist during the first two. Freeze individually wrapped slices for up to 1 month.

Safety notes

Do not taste the raw batter, which contains raw egg and flour. The cake bakes through fully. Contains wheat, egg and milk.