Cashews aren't nuts in the botanical sense, but they have enough similarities when it comes to texture, appearance and taste that the term fits -- unless you're making nut flour. Cashews get gummy and turn to nut butter when you grind them -- not a bad thing, but the opposite of what you want in a flour. Making nut flour with cashews requires a few extra steps than making flour with almonds or hazelnuts, for example, but you get a more refined product -- and a few byproducts, such as velvety cashew milk -- as a result.
Soak the raw cashews overnight in twice as much water by volume, or 2 cups of water for every cup of raw cashews. You need about 1 cup of raw cashews to make 3/4 cup of nut flour.
Grind the cashews with the soaking water in a food processor until creamy and smooth, about 2 minutes.
Transfer the cashew paste to a fine-mesh sieve lined with 2 layers of cheesecloth and place over a bowl.
Drain the cashew paste for about 5 minutes, then press on the solids with the back of a spoon or a rubber spatula. The remaining solids are referred to as cashew pulp.
Squeeze out the excess moisture from the cashew pulp by bringing the 4 corners of the cheesecloth together and wringing them out. Transfer the cashew nut milk to an airtight storage container and keep it in the refrigerator up to 2 days. Use cashew nut milk in drinks and baked goods.
Spoon the cashew nut pulp from the cheesecloth and place it in a pile on a baking sheet lined with parchment paper.
Spread the cashew pulp over the parchment paper in a thin, even layer using an offset spatula or a rubber spatula. Make the layer and uniform as possible so it will dry evenly.
Move the oven rack to the top position and snap a grill thermometer onto it. Set the oven to 140 degrees Fahrenheit or the lowest setting.
Fold a kitchen towel several times and wedge it in the oven door to prop it open about 4 inches. Let the oven heat for 10 minutes.
Check the temperature on the grill thermometer. The goal temperature is 105 F, but if you can get it to between 100 and 110 F, don't change a thing. If the temperature is higher than 110 F, prop the oven door open about 1 inch more to bring the temperature down a bit. If the temperature is under 95 F, unfold the towel once to close the oven door a little more and raise the temperature.
Dry the cashew pulp until it desiccates and dries completely, about 24 hours. Transfer the dried cashew pulp to a spice or coffee grinder and grind it in batches until it reaches a fine, silty consistency.
Store cashew flour in an airtight container in the refrigerator for up to 2 days.