First of all I have to inform you that I was raised on chestnuts, and chestnut flour. We made many things with the flour, mostly fritters (you can find the recipe here) and castagnaccio. There are so many versions of castagnaccio, the main being just chestnut flour and water, with a pinch of salt (optional) and a sprig of rosemary on the top. The best thing is that chestnut flour is naturally sweet, and that you just need water to mix it, making it the perfect low fat (chestnuts are the only low fat nuts) high protein, gluten free and vegan treat!
I mixed chestnut flour with enough water to make a batter, and this time I added 2 tbsp of cocoa (cocoa also go well with chestnuts) and a very small pinch of salt. No sugar needed. Pour the batter into a large baking pan lined with baking paper and bake everything at 180°C until the cake is ready (about 20 minutes, check with a toothpick). Let it cool down before serving. Unfortunately I forgot to take the photo on the first day, so this was the morning after and the top of the castagnaccio had cracked like a dry desert... but it was still great for breakfast :-).