This recipe is very easy to do and though it is not cheap the results are spectacular. There are some versions of Castanhas Bolo employing wheat flour so is not so expensive but if you have the opportunity to test a chestnut cake made entirely with chestnut flour literally you will "freak out".
2 kg (4.4 lb) of chestnuts (800 grams - 20 oz - of chestnut flour)
Half a kilo of sugar (17.6 oz)
250 grams of butter (8.8 oz)
2 teaspoons vanilla extract
First we will make the chestnut flour. It is true that in some places they sell it ready-made, but it is often difficult to find.
Preheat oven to 200 ºC (392 F). We make an indentation in the skin of the chestnuts (this is important). We place them on a tray and introduce into the oven for about 40 minutes. After that time we took them and check if it easy to separate the skin from the pulp and let cool to room temperature. If not easy, give some extra time.
When the chestnuts are cold we took them to the freezer and leave it for an hour. Thus they will be made hard enough so that we can reduce to flour with the help of a coffee grinder or similar. 2 kg (4.4 lb) will be around 800 grams 20 oz - of chestnuts' flour. If flour obtained is above 800 gr/20 oz, remove the excess quantity till get the right weight. In case to obtain less quantity, simply add wheat flour.
Then you mix melted butter with the sugar with the aid of an electric mixer. When the mixture is smooth, add eggs slowly, stirring constantly, and then the vanilla extract.
The mixture is poured into a bowl and now it's time to incorporate chestnut flour. It is mixed with rods, do not use an electrical accessory. You will gradually add the flour and mix to obtain an homogeneous mass.
We paint with butter the mold and scatter some flour to make easy unmold, or we employ a silicone mold and those two previous steps are unnecessary. Pour the batter into the mold.
Preheat oven to 180 degrees c (350 F) and let it cook for 40 minutes. After the 40 minutes, remove from oven and let rest till cake gets room temperature. Accompanied by some whipped cream is delightful.
The chestnut flour can be made another day and store in the refrigerator for several weeks.