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1
Combine the chestnut flour, plain wheat flour, and bread flour in a large bowl. Whisk briefly to distribute evenly. The chestnut flour constitutes 40% of the total flour weight — the upper limit of the range that yields a workable gluten structure with full chestnut character.
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2
Dissolve the yeast in the lukewarm water and leave for five minutes. Pour into the flour mixture along with the salt and olive oil. Mix until a shaggy dough forms, then knead on a lightly floured surface for eight to ten minutes. The dough will be denser and less extensible than a pure wheat dough; this is correct. Stop when the dough is cohesive, tacky rather than sticky, and holds its shape when pressed into a ball.
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3
This is where the bread lives or dies. Place the dough in a lightly oiled bowl, cover tightly, and refrigerate for 12 to 16 hours. The extended cold fermentation allows the chestnut starch to hydrate fully and the yeast to work slowly through a medium it metabolises more slowly than pure wheat starch. A shorter proof will leave the crumb gummy at the centre; a longer one beyond 16 hours risks over-fermentation. At the end of fermentation the dough should have increased by roughly half and smell yeasty and faintly sweet — not sour, not flat.
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4
Remove the dough from the refrigerator and allow it to come to room temperature for one hour. Shape into a round or oval loaf and place on a floured baking sheet or in a floured proving basket. Cover and prove at room temperature for a further 45 to 60 minutes, until the dough is slightly puffed and a floured finger pressed gently into the surface leaves an indentation that springs back slowly but does not collapse.
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5
Heat the oven to 220°C (or a wood-fired oven at equivalent temperature) with a heavy baking surface inside. Score the top of the loaf with a sharp blade in one or two decisive cuts. Slide the loaf onto the hot surface and bake at 220°C for the first fifteen minutes to drive oven spring and begin crust formation — the loaf should audibly hiss and the cut surfaces should open and colour to dark beige-brown.
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6
Reduce the oven temperature to 190°C and bake for a further thirty-five minutes. The loaf is done when the crust is a deep, even dark beige-brown across the surface, the underside sounds hollow when tapped with a knuckle, and the crust crackles when pressed lightly at the sides.
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7
Transfer to a wire rack and cool for a minimum of one hour before cutting. The crumb continues to set as it cools. Sliced correctly, the crumb should be dense and moist with no gummy patches, dark beige-brown throughout, and hold its structure cleanly at the cut face.