Things You'll Need
Filtered water or spring water
Nut-milk bag or cheesecloth and fine-mesh sieve
Food dehydrator and nonstick drying sheet
Parchment paper and sheet pan (optional)
Making chestnut flour requires finesse. Unlike other nut flours, such as almond, that you can simply grind into a coarse meal and call it a day, you have to coax chestnuts into a fine flour from start to finish. But when you process chestnut flour to a dry, silky consistency, you can use it in dishes too refined for coarse, mealy flours, such as gnocchi, crepes and clafoutis.
Peeling and Preparing
Slice each chestnut in half vertically, from the pointed tip to the rounded bottom. A sharp, heavy chef's knife works best. Work in 1-pound batches of unshelled chestnuts.
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Bring a few quarts of water to a boil in a large pot; you need enough water to cover the chestnuts by at least 1 inch. Add 1 pound of halved chestnuts to the boiling water.
Blanch the chestnuts for 7 1/2 minutes and drain them in a colander under cold running water. Let the nuts drain in the colander for a few minutes and transfer them to a bowl.
Drop the chestnuts from their shells into a separate bowl. Extract the nuts that don't fall out readily with the tip of a paring knife.
Cover the chestnuts with filtered water or spring water and let them soak for 10 to 12 hours.
Transfer the chestnuts and the water to a blender or food processor. Process the chestnuts until smooth; work in batches, if necessary.
Scrape the pureed chestnuts from the blender to a nut-milk bag set over a bowl. You can also pour the chestnut puree into a sieve lined with two or three layers of cheesecloth set over a bowl.
Let the chestnut milk drain into the bowl for about 5 minutes; then press the solids using a rubber spatula. Wring the remaining chestnut milk from the bag or cheesecloth. Store the chestnut milk in an airtight container for up to three days in the refrigerator.
Scrape the chestnut pulp onto a nonstick drying sheet and spread it in an even layer, no thicker than 1/4-inch thick, using a spatula. Dry the pulp in a food dehydrator for 24 hours at 105 degrees Fahrenheit.
Alternatively, spread the chestnut pulp in an even layer on a sheet pan lined with parchment paper. Dry the pulp in the oven on the lowest setting for 24 hours or until it's completely dry; use a towel or oven mitt to keep the oven door propped open about 1 inch.
Transfer the dry chestnut pulp to a spice grinder and process it into a fine powder. Store chestnut flour in the refrigerator for up to three days.
Replace up to 20 percent of the wheat flour in any recipe with chestnut flour.