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covered, warm room, about 25°C

yeast + sugar + half the warm milk + all the buckwheat flour, whisked to a loose sponge — milk hotter than a fingertip can stand kills the yeast outright, and cold milk simply stalls it. Buckwheat goes in first because it is the slowest to hydrate and its flavour is what the long ferment is for; the sponge is ready when the surface is domed and pocked and smells faintly of beer