This is a recipe taken from a restaurant in a little town in Lazio, Italy, where chestnuts are a staple of the local cuisine. The recipe was mounted on the restaurant wall in a framed poster, and I took a picture of it and translated it from Italian.

As usual I didn’t use precise measurements, so you don’t have to either. All proportions are approximate, so don’t worry about it! 

1 bag dried chickpeas (about 5 cups dried) 
2 bags cooked chestnuts (about 4 cups)
1 small can of tomato paste
two big sprigs rosemary
5 stalks celery, diced fine 
Some great olive oil 

Put the dried chickpeas in salted water and bring them to a boil. Reduce the heat and cook them for an hour or two until they are very soft. Then let them sit until they get to room temp. I let them sit overnight but a few hours would do it. Do not drain the chickpeas; the water they cooked in is an important element of the soup.
I used already-cooked chestnuts in my soup since I brought them back from Italy. They were whole in the package, so I cut them up on a cutting board so they would be about the same size as a chickpea. The basic proportion you want for the soup is 2/3 chickpeas, 1/3 chestnuts. 
Take some of the cooled cooked chickpeas (a cup or two) and put them in a food processor, along with a couple handfuls of the cooked chestnuts. Add some water and the can of tomato paste, and blend until it’s pureed. You may have to add a little more water to thin it out. 
Then add the pureed beans to the cooked chickpeas in your soup pot, and add in your chopped chestnuts. Toss in the diced celery and the sprigs of rosemary, and salt and pepper the soup. 
Cook this over a low heat until the rosemary falls off the stems. You will have to stir it every few minutes or so to avoid it sticking to the bottom. 
Once the rosemary leaves have fallen off the stems, check the soup for seasoning, as it may need more salt and pepper. At this point you may also want to puree more of the chickpeas and chestnuts if you want a less chunky soup. I like to have a thick base with nice chunks of chestnuts and chickpeas inside, but that proportion is up to you.
Ladle the soup into bowls and top it with some great extra virgin olive oil. 
This soup is vegan but it doesn’t taste like it. Our guests could not believe there was no meat broth in it; it’s a very hearty and flavorful soup, and it’s so easy to make, I honestly can’t imagine how you could mess it up! 

Buon appetito!!