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1
Soak the kanten powder in the measured cold water for five minutes, then bring to a full boil in a heavy saucepan, stirring until the kanten is completely dissolved. The liquid will turn clear; any cloudiness indicates undissolved kanten, which will compromise the final set.
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2
Add the sugar and stir over medium heat until fully dissolved. Reduce to a low simmer. The kanten ratio — 3% of liquid weight for neri-yokan — is the fundamental technical variable of the entire confection. Too little kanten yields a mizuyokan; too much produces a chalky, over-firm bar. This is where the dish lives or dies.
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3
Add the anko to the kanten syrup and stir continuously over low heat until fully incorporated and the mixture thickens to a heavy, slow-falling consistency. For the matcha variant, sift ceremony-grade matcha into the hot mixture at this stage and stir rapidly to minimise air exposure; the colour should be a deep, unoxidised green.
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4
Pour the mixture into a damp rectangular mould — a standard nagashi-kan or any loaf mould lined with damp parchment. For the kuri variant, allow the surface to cool until barely set, then press blanched whole chestnuts into the bar at even intervals before the set is complete. The surface should show no bubbles or ripple marks.
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5
Allow to cool at room temperature until fully set. The bar will pull slightly from the sides of the mould and hold its form cleanly when unmoulded onto a board. Neri-yokan requires no refrigeration and will hold for weeks at cool room temperature; mizuyokan (made at 2% kanten) must be refrigerated and served well-chilled.
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6
To slice, dampen the blade of a thin knife with water before each cut. Draw the blade through in a single, unhurried stroke. A dry blade drags and tears the surface; the dampened blade should produce a clean, translucent face with no crumbling at the edge. Slice to hafu-pon thickness for tea ceremony service.