I forgot to mention that I used pre-cooked vacuum packed beetroot instead of roasting one beet and it worked really well — good if one hasn't a lot of time.
You can also buy sweetened or unsweetened chestnut purée; pre-cooked, vacuum - packed chestnuts; and preserved candied chestnuts, aka marron glacè, all of which, in contrast to raw chestnuts, are ready to use or eat straightaway.