Khanom Thuai Fu (ขนมถ้วยฟู)

The Cake That Must Flower

ขนมถ้วยฟู is judged by its top: the batter rises in the steam until the surface cracks open like a flower — ฟู means to swell and prosper, which is why the little cups are stacked at weddings, housewarmings and shrine offerings. TrueID's article spells out the belief: the risen, flowering cake stands for เฟื่องฟู ความเจริญงอกงาม และความรุ่งเรือง — flourishing, growth and prosperity.

The rise is fermentation, not just baking powder. Every rice-flour version blends cooked jasmine rice into the batter — Kapook uses 160 g, Sangwun 120 g, one Wongnai home cook just 40 g in a small batch — then rests it under plastic wrap for two to three hours until the yeast works and the batter turns frothy. Aroimak notes the ancient version skipped baking powder entirely and used a fermented rice starter, a recipe its shop has sold for seventy years.

There is a naming split. Wongnai's home cook and Aroimak are explicit: ถ้วยฟู is built on rice flour — dense and chewy — while ปุยฝ้าย (cotton-fluff) is built on cake flour with eggs and SP emulsifier, light and airy. TrueID's recipe is titled ปุยฝ้าย "หรือขนมถ้วยฟู" — treating the two as one family, which is how most markets sell them: the same little cup, the same flowered top, a different bite.

The Recipe (rice-flour version, from Kapook / Aroimak)

The small batch (Wongnai): 105 g rice flour, 40 g cooked jasmine rice, 85 g sugar, ¼ tsp yeast, 1 tsp baking powder, 200 g water, ¼ tsp jasmine essence. The shop batch (Sangwun, 68 cups): 315 g rice flour, 24 g arrowroot flour, 120 g cooked rice, 255 g sugar, ¾ tsp yeast, 1 tbsp baking powder, 500 g jasmine water. The fluffy cousin (TrueID, ปุยฝ้าย): 450 g cake flour, 2 tsp baking powder, 400 g sugar, 400 g cold water, 15 g SP, 2 eggs, ¼ tsp jasmine essence, 2 tsp lime juice — whipped, no fermentation.

The Method

1. The rice. Blend the cooked jasmine rice with a little water until completely smooth — this is what gives the cake its chewy, dense bite.
2. The jasmine water. Mix the water with the jasmine essence, or use jasmine-flower water (น้ำลอยดอกมะลิ) as the traditionalists do.
3. The batter. Put the rice flour in a mixing bowl with the sugar, baking powder and yeast, add the blended rice and knead, pouring in the jasmine water gradually until it is all incorporated into a smooth batter.
4. The rest. Divide into bowls and colour each as liked, cover with plastic wrap and rest 2–3 hours until the batter rises and turns frothy. This is the step that makes the top flower — skipping it means a flat, dead cake.
5. The steam. Fill the little cups (ถ้วยตะไล) and steam over high heat about 20 minutes, until the surface cracks into a flower. Cool before unmoulding — a warm cake tears.

Where Thai Sources Disagree

How Western Versions Get It Wrong

• Baking it. Khanom thuai fu is steamed, never baked — an oven crust kills the flowered, moist top that defines the cake.
• Skipping the fermentation. The two-to-three-hour yeast rest is the recipe. Whisking baking powder into rice flour and steaming immediately gives a flat, gummy puck, not a risen cake.
• Leaving out the cooked rice. The blended cooked jasmine rice is what separates ถ้วยฟู's dense chew from a generic steamed sponge. Every rice-flour source includes it.
• Treating ปุยฝ้าย as interchangeable. The cake-flour, egg-and-SP version is a different cake. Calling either by the other's name is the one mistake Thai sources actively correct.
• Unmoulding warm. The cakes must cool in the cups first — a warm ถ้วยฟู tears on the way out and never flowers again.

UK Ingredient Notes

• Rice flour: standard in UK supermarkets' free-from sections and every Asian grocer.
• Arrowroot flour (for the Sangwun version): at Thai grocers, or skip it — Kapook's blend has none.
• The little cups (ถ้วยตะไล): small ceramic ramekins or soy-sauce dishes work; the batter should fill them shallow so the top flowers fast.
• Jasmine essence: at Thai grocers; or infuse a few jasmine tea bags in the water for the traditional scent.
• Steaming setup: any lidded pot with a trivet and a tea towel tied around the lid to catch drips — drips pock the flowering tops.

Sources

This recipe is translated from the following Thai-language sources. Where they disagree, we've said so.