 As a British transplant to the USA, I love Thanksgiving. But since moving here over 13 years ago, I've had a hard time getting my head around the Thanksgiving dish known as Candied Yams. For the uninitiated, this is how it works. Take a bunch of sweet potatoes, bake them until they're soft and scrumptious, add sugar, lots of it, preferably maple syrup, mix in lashings of butter, then top the whole sticky sweet concoction with, wait for it, Marshmallows, and bake until they just begin to caramelise. The sheer audacity of a dish that starts with a sweet vegetable, adds mountains of sugar and butter and then tops everything off with even more sugar is impressive. And then to serve it as an accompaniment to turkey and stuffing, outstanding. Having had my brains bamboozled by this tradition for the past 13 years, I thought it was time to delve into its history, or rather ask my grad student to do some background digging. Most records trace back cultivation of the sweet potato, which actually isn't a yam, but that's another story, to Peru, nearly 3,000 years ago. By the time Christopher Columbus stumbled onto the Americas many centuries later, it was an established part of the diet over this side of the Atlantic. Like many other delicacies, the sweet potato found its way across the Atlantic and into British cuisine in the 1500s, where it got a bit of a reputation as an aphrodisiac. But instead of sugar, vinegar, salt and prunes seemed to be the additions of choice here. Back in the US, sweet potato rapidly became a staple of household cooks, and for some reason, one that called out for yet more sweetness. By the late 1800s, recipes were being preserved that called for adding a pound of sugar to every pound of sweet potato. And why stop there? Recipes from the time show cooks throwing in sugar, butter, cream and anything else that tastes good, but probably isn't, into their sweet sweet potatoes. You'd think that with all this sweet creamy succulents, marshmallows wouldn't stand a chance, but you'd be wrong. In 1917, the marketers of Angelus Marshmallows hired the founder of the Boston Cooking School magazine, Janet Hill, to develop recipes designed to encourage home cooks to embrace marshmallows. The recipe booklet that came out of this contained the first documented recipe for baked sweet potatoes topped with marshmallows, and the rest, I guess, is history, sort of. To be honest, it still isn't clear to me why this took off, and why it's so closely associated with Thanksgiving. Pure speculation would hazard that the sheer decadence of the candied sweet potatoes makes it a great delicacy for special occasions. What remains as an even bigger mystery to me, though, is who in their right mind would serve this with turkey and stuffing. But then, this country is nothing if not innovative. Happy Thanksgiving.