Many traditional gluten-free cakes are made with nut-based flours. Almost any nut can be ground into flour (or "meal", if the skin is still on the nut). While most nut flours can be purchased in stores or online, some may be difficult to find or too expensive to buy. Grinding nuts on your own is fairly simple, but you have to avoid pulverizing the nut for too long in a food processor or it can quickly turn from a nut flour into a creamy nut paste. Here are some tips to aid the process. This guide works for practically any kind of nut.
Blanching is a process that removes the skin from a raw nut using boiling water. The skin may need to be removed as it either can affect the appearance or texture of the final product. This process is followed to make almond or hazelnut flour. Most other nuts are ground with the skins on them. Almonds and hazelnuts also can be ground with the skins which is then called "meal"; almond flour is more commonly used as it has a finer texture and lighter color than almond meal.
To blanch almonds or hazelnuts, fill up a pot about half full with water and bring to a boil. Add the almonds or hazelnuts to the boiling water and remove them with a sieve as soon as the skins start to look wrinkled (about 30-60 seconds for almonds and 2-3 minutes for hazelnuts). Rinsing them under cold water and placing them on a baking sheet or dish to cool. Do not boil them for too long or they will lose their crispness. Pat the nuts dry with a clean towel and immediately remove their skin by squeezing the nut between your index finger and thumb. You also can rub the nuts in a clean towel to remove the skin. Remove any leftover skin with a small, sharp knife. If the nuts become cool and dry again, it will become harder to remove the skins and you may need to boil them again.
Before grinding to make almond or hazelnut flour, the skinless nuts must be completely dry. Do not skip this step. Line a baking sheet with some paper towels, place the blanched almonds or hazelnut on the towels and let them dry for 4-6 hours or overnight.
Roasting nuts deepens their flavor, making them even more nutty and complex. If the recipe calls for roasted nuts, toast them in the oven before grinding or chopping. Spread the nuts in an even layer on a baking sheet and place in a pre-heated oven at 175C (350F) for 7-10 minutes. Roasting nuts can be a little tricky as they can go from almost done to overdone in less than a minute and some nuts (e.g. pine nuts) may roast faster than others. It is important to check the nuts frequently and stir them often to ensure that they are evenly toasted. When the nuts are browned and smell fragrant, remove from the oven and immediately transfer onto a plate or another baking sheet. Do not cool the nuts on the tray they were baked on or you will risk scorching them. Make sure the nuts are fully cool before using them.
To make a nut flour or meal, make sure the components of the blender or food processor (blade, bowl) are dry and at room temperature (not hot from the dishwasher). You can use raw or toasted nuts as indicated in the recipe. The nuts should also be at room temperature. Only grind about 70 grams (about ½ cup) at a time. Pulse on and off for about 10-15 seconds until the nuts are as finely ground as you like, shaking or scraping the sides of the bowl from time to time. The time will vary based on the blender or food processor. Avoid grinding the nuts for too long or it will be become a nut butter. It may be useful to add a spoon of sugar from the recipe to keep the nuts from turning into butter.
Store your nuts and nut flours/meals in an airtight container in a dark, cool place or preferably in the refrigerator or freezer to avoid rancidity. Homemade nut flour/meal has a shelf life of a few months (or a year in the freezer). If the nut flour tastes and smells bitter, it has gone bad and it needs to be thrown out.
Since nut flours are higher in fat and do not contain gluten-forming proteins, they must be used with other ingredients which contribute to the structure of the baked goods. Most nut-based recipes rely on whipped egg whites for that structure. For more information, check out the page on Whipping Egg Whites.