It is easy to make Chestnut Soup with any recipe that already has potato's in it. I make at least one batch of chestnut soup a year since i have so many chestnuts around being a chestnut grower. My favorite chestnut soup is Chestnut leek soup. The last one i made this year was both chestnut and potato leek soup. I just used one potato instead of two and substituted chestnut meat for one of the potato's. It took around 20 chestnuts which i flash cooked after making holes in them in the microwave oven. The recipe is in any cook book or your own. Just precook the chestnuts peal and get the inner skin off too, mash or dice and add to the boiling soup base instead of all the potato's or just some of them.
The approximate recipe i use for chestnut leek soup is:
6 cups of water
20 chestnuts precooked and mashed from the microwave and one yellow potato or 4o chestnuts and no potato
3 leeks pan fried before boiling with light oil
a half of a carrot diced
a bay leaf, thyme, pepper, salt and other spices to taste
Several drops of Aromatic bitters used for flavoring cocktails
3 garlic sections mashed from a fresh clove or garlic powder.
This is the basic recipe and it is boiled until it has the consistency of a melded soup.
You can use any recipe with chestnuts instead of potato's including making a chestnut clam chowder as one of the more unusual sounding suggestions. Any potato soup recipe can become a chestnut bisque instead by substituting all or just some of the the potato's for chestnuts.