Castagnaccio is a cake that is made primarily with flour derived from ground chestnuts. It is often referred to as chestnut cake. The dessert is traditionally served in the cuisine of Tuscany, a region located in northern Italy that has an abundance of chestnuts. The cake tends to be considered to have a distinctive taste that is rich and nutty, rather than overtly sweet due to the small amounts of sugar and other sweetening agents that are used.
Chestnuts, the main ingredient in traditional castagnaccio cake, are a variety of nut that grows on chestnut trees and must be boiled, roasted, or otherwise cooked prior to consumption. This is due to them containing tannic acid, a naturally occurring plant chemical that can cause digestive discomfort. In order to be used in the cake recipe, the chestnuts are ground into a flour. Chestnut flour is generally available in Italian specialty stores or can be homemade by grinding the chestnuts with a mortar and pestle or food processor until the nuts form a powder.
Although the chestnut flour is generally the primary ingredient in castagnaccio, it also contains other basic ingredients. The cake base has a thin texture that usually consists of water and small amounts of salt, sugar, or olive oil, mixed with the chestnut flour to form a batter. If sugar is used, it is typically only about 2 tablespoons (30 ml) to just add a hint of sweetness to counteract the richness of the chestnuts. Chopped nuts, raisins, chopped rosemary sprigs, or citrus zest may also be added to the batter for additional flavor.
The process of making castagnaccio typically begins with mixing the chestnut flour and water and whisking or beating it until no lumps remain. The exact ratio may vary depending on the desired thickness or diameter of the cake, but a standard ratio is often two parts chestnut flour to one part water. Any nuts, raisins, citrus zest, or other additional ingredients are usually added into the batter and stirred by hand after the flour and water base is prepared. The batter is then baked in a greased pan for approximately 30 to 40 minutes.
Once baked, castagnaccio remains a flat cake that does not rise much during the cooking process. It is traditionally served at room temperature or cold, rather than fresh from the oven. Due to its strong, more savory taste, it is often paired with wine rather than the coffee that is often served with sweeter cakes and desserts.