Banh Da Lon — layered tapioca-pandan cake

i. Origin & history

The cake belongs to the family of Southeast Asian steamed layer cakes, and its closest relatives are Indonesian and Malaysian: kue lapis and kuih lapis work on exactly the same principle of building a cake from thin layers steamed one at a time. The shared technique across the region reflects shared ingredients — rice, tapioca, coconut, pandan — and shared equipment, since a steamer is a far more common household tool than an oven.

The name is worth explaining because it puts people off. Bánh da lợn translates literally as 'pig skin cake', and the reference is to texture rather than to any ingredient. The cake's springy, slightly gelatinous, translucent quality was thought to resemble the texture of pork skin. There is no pork in it; it is entirely plant-based.

It is southern Vietnamese in its strongest associations and is street and market food rather than restaurant dessert — sold by the tray, cut into diamonds, eaten in the afternoon. It also travelled with the Vietnamese diaspora and is a standard item in Vietnamese bakeries in the United States, France and Australia.

The classic pairing of pandan with mung bean is not arbitrary. Pandan supplies aroma and colour but very little body; mung bean supplies a soft, faintly nutty, starchy substance but no colour. Alternating them gives both visual contrast and a genuine difference in texture between the layers.

ii. Tapioca starch, and steaming in sequence

The chew is the whole point of this cake, and it comes almost entirely from tapioca starch.

Tapioca starch gelatinises into a notably elastic, springy, translucent gel — far more so than rice flour or wheat flour, which give softer and more crumbly results. Bánh da lợn typically uses a high proportion of tapioca starch, often with some rice flour to temper it, and the ratio between them is the main lever on texture. More tapioca gives a chewier, glossier, more translucent cake; more rice flour gives a softer, more tender, more opaque one. Tapioca alone is unpleasantly rubbery.

The layers form because each is steamed to setting before the next goes on. A thin ladleful of batter goes into the hot steamer, sets in five to seven minutes, and the next colour goes directly onto it. There is no assembly and no folding.

The bonding between layers depends on timing. Each layer should be steamed until it is just set but still slightly tacky on the surface — that tackiness is what the next layer grips. Steamed until fully dry, the surface will not bond and the finished cake separates into loose sheets when cut. Not steamed enough, and the next ladleful blurs into it.

Two practical points. The batter separates rapidly as it stands, since tapioca and rice starch settle within a couple of minutes, so it must be stirred before every single ladleful. And condensation from the steamer lid will pit the surface of each layer unless the lid is wrapped in a cloth — a standard precaution for all steamed Asian cakes and one that makes an immediately visible difference.

iii. Ingredients

Makes 12 servings · scroll the side panel to adjust

• 200 g cooked split mung beans, mashed
• 100 g rice flour
• 100 g tapioca starch
• 250 g sugar
• 800 ml coconut milk
• Pinch salt
• 60 ml pandan juice
• Yellow food colour (optional)

Tapioca starch is what gives the chew and cannot be replaced by cornflour, which sets soft and cloudy. A proportion of rice flour keeps it from being rubbery. Split hulled mung beans must be soaked and cooked until completely soft, then blended smooth — undercooked beans leave a gritty layer that nothing can fix. Full-fat coconut milk is most of the flavour. Pandan extract from fresh or frozen leaves gives the correct aroma and a soft green; pandan paste gives the brighter colour most people expect. A pinch of salt in both batters is essential against the sweetness.

iv. Method

1. Combine rice flour, tapioca starch, sugar and salt; whisk in coconut milk to a thin smooth batter; divide in half.
2. Mix mashed mung beans into one half (the yellow layer). Add a touch of yellow colour if desired.
3. Mix pandan juice into the other half (the green layer).
4. Lightly oil a 22 cm round tin. Steam empty 5 min.
5. Pour a 5 mm layer of green; steam 5 min. Pour 5 mm yellow; steam 6 min (the mung-bean layer takes slightly longer). Alternate until you have 6-8 layers.
6. Steam the finished cake 10 more min. Cool fully (4 hours) before cutting into diamonds.

v. Tips & common mistakes

• Stir the batter before every ladleful. Tapioca and rice starch settle to the bottom within a couple of minutes. Without re-stirring, early layers come out dense and later ones thin and watery.
• Steam each layer until just set and still tacky. Five to seven minutes. A fully dried surface will not bond to the next layer and the cake will fall apart into sheets when cut; an under-set one blurs into the layer above.
• Wrap the steamer lid in a cloth. Condensation dripping onto each layer leaves pits and patches. The cloth absorbs it, and the improvement is immediately visible.
• Cook the mung beans until they collapse. Soak them for several hours and cook until completely soft, then blend until smooth. Gritty mung bean paste is the most common flaw in a home-made bánh da lợn and cannot be corrected later.
• Keep the layers thin and consistent. Use the same small ladle every time. Thick layers do not set through, and unequal ones spoil the effect the whole cake exists for.
• Cool completely before cutting, and oil the knife. Several hours. Cut warm, it drags and tears; cut cold with an oiled blade, it gives clean diamonds with sharp stripes.

vi. Variations

The classic is pandan and mung bean. Taro versions substitute purple taro paste for the mung bean, and durian versions are popular in the south. Some versions use butterfly pea flower for blue layers, or palm sugar for brown ones. The number of layers varies from four to a dozen or more. Regional relatives include Indonesian kue lapis and Malaysian kuih lapis, which use the same sequential steaming with slightly different starch ratios, and khanom chan in Thailand.

vii. Serving & storage

Bánh da lợn is served at room temperature, cut into diamonds or squares, as an afternoon snack with tea or Vietnamese coffee rather than as a dessert course. The traditional pleasure is peeling the layers apart with your fingers and eating them one at a time, which is why the bonding between layers matters — they should separate cleanly but not fall apart on their own.

It is best on the day it is made. Keep it at room temperature under a cover and do not refrigerate it: tapioca and rice starches retrograde in the cold, and the cake turns hard, dry and grainy within a few hours. This is the single most common way a good bánh da lợn is ruined. If it has been chilled, steaming the slices for two or three minutes will restore most of the original texture. It does not freeze well for the same reason.

ix. More from Vietnamese

• Khanom Chan — Thai layered rice cake
• Kue Lapis — Indonesian layered cake
• Seri Muka — two-layer pandan rice cake
• Sapin-Sapin — Filipino layered rice cake
• Bebinca — Goan layered coconut cake
• Klepon — Indonesian palm-sugar balls