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1
Separate the duck egg yolks from the whites, then pass the yolks through a fine-mesh sieve into a clean bowl, pressing gently. Repeat the straining once more, so that every fragment of membrane and chalaza is removed — any trace left behind will block the sieve holes at the pouring stage and break the threads before they form. The strained yolk must be completely smooth and flow like heavy cream when the bowl is tilted.
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2
Combine the palm sugar and water in a wide, shallow pan, add the jasmine flowers, and bring to a simmer over medium heat, stirring only until the sugar dissolves. Continue to cook without stirring until the syrup reaches exactly 110 °C on a thermometer — at this point the surface carries a fine, even shimmer and a drop tested on a cold surface holds a soft, pliable thread. This is where the dish lives or dies: below 110 °C the egg threads will not set and will float as loose strands; above 110 °C they will toughen on contact with the syrup.
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3
Remove the jasmine flowers from the syrup so they do not catch on the threads during pouring, then keep the pan over the lowest heat that holds the temperature steady at 110 °C. Transfer the strained yolks to a jug or squeeze bottle fitted with a fine-holed sieve or a traditional foi thong cone — a tin cone with 3–5 holes of approximately 1–2 mm diameter — and hold the vessel 20–25 cm above the surface of the syrup so the threads have room to thin and lengthen before they meet the heat.
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4
Pour the yolk in a single, continuous, confident circular motion over the surface of the simmering syrup, moving the vessel in steady concentric passes without pausing, so that each strand forms unbroken from start to finish — any stop or restart creates weak points that snap when you lift. The threads set within seconds of contact with the syrup, turning a deep, even gold across their entire length.
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5
Lift the set threads immediately from the syrup using two thin skewers or chopsticks, drawing them clear in a single gathering motion and draining briefly over the pan, so excess syrup falls away rather than pooling and gluing the strands together. The threads are done when they hold their form without sticking to one another and carry a uniform golden colour with no pale or cloudy patches.
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6
Arrange the threads on a serving plate or fold them into loose nests, then repeat with the remaining yolk in successive passes, maintaining syrup temperature throughout so each batch sets at the same speed and colour. The finished foi thong should be hair-thin, glossy, and distinctly fragrant with jasmine.