I am thinking up ways to prepare them. The simplest would be to boil them up and serve with butter, salt, pepper, and maybe some rosemary. I'm also thinking about using them for a Spanish Tortilla. Or maybe roasting them to make some little round "fries". Seems like a fun snack food! They're just about the size of a Junior Mint. You could sneak some in your bag and take them to the movies!
I've read that the large taproot is a staple crop in Japan, and quite delicious. But we don't really have enough plants to go eating their taproots. So, we'll enjoy the "berries". I'm waiting till next week to cook with them (we have a video shoot at our house and want to keep them on the vine for that). I will let you know how my experiments turn out!
(photo of taproot, leaves, yam berries, and pruners for scale)