How to make the perfect Thanksgiving sweet potato casserole

Adding sugar is a must, but should you boil your sweet potatoes or bake them? And are eggs essential? Then there is the dilemma over toppings. Marshmallows, anyone?

Perfect sweet potato casserole. Photograph: Felicity Cloake for the Guardian

When I asked an American friend what people do to celebrate Thanksgiving, he said that, mostly, they ate. And when they weren’t eating, they were watching football. No church, no gifts, just good food and thankfulness.
And what food! Deep-fried turkeys and pumpkin pies, cornbread stuffing and cranberry relish – and (most exotic of all to these British eyes) candied sweet potatoes, a dessert that has somehow fought its way on to the main course of the biggest meal of the year. Though the sweet potato has been an important part of the continent’s diet for millennia, and early European settlers readily adopted it as a pie filling, the Thanksgiving casserole’s infamous marshmallow topping didn’t appear until the early 20th century, apparently at the behest of interested candy manufacturers.
Sugar and gravy might not be a combination that every American is thankful for, however – Jane Nickerson, writing in the New York Times in 1948, prefaces her recipe with the underwhelming declaration: “I am not a fan, but about 250,000,000 Americans are, so here is my faint nod to their mystifying tastes.” I’m going to out myself – this week I discovered that, though I’m not American, I am a bit of a fan of candied sweet potatoes. Which just goes to show that you should try something before you knock it.

Cooks Illustrated’s candied sweet potato. Photograph: Felicity Cloake/Guardian

The potatoes

Like most tubers, the dense sweet potato requires some serious cooking. Early recipes often boil them in their skins, something also advocated by the classic Joy of Cooking, but the Cook’s Illustrated All-Time Best Recipes warn that this yields a wet texture and a “mild, watery flavour”. They’re right; the Joy may be a bible of American cooking, but its sweet potatoes remind me of boring old boiled carrots.
Instead, Cook’s Illustrated braises the potatoes in a mixture of cream, butter and sugar while Chow goes for a sugar syrup and butter mixture instead – both using just enough liquid to cook the vegetables through, but not enough to wash out their flavour. The Cooks Illustrated version, which eschews water altogether, is better, but it’s still not as good as the baked varieties I try.
Saveur and Southern Living magazines both bake their sweet potatoes in their skins before peeling and mashing them. If you can afford the power, this method yields an intensely sweet, full-flavoured result; sweet potatoes that taste almost ridiculously of themselves. Chow and Joy of Cooking both serve their sweet potatoes in slices, rather than mashing or puréeing them, as other recipes suggest. I think this is a mistake; one of my favourite things about this tuber is its velvety texture when puréed. This also means that the Chow version hasn’t absorbed much of the buttery, sugary flavour of its braising liquid, remaining sweet potato chunks in sauce. Far less satisfactory.

Saveur’s sweet potato casserole. Photograph: Felicity Cloake/Guardian

The fats

Butter is obviously a must here – you can’t have mashed potato of any stamp without it. Southern Living adds milk too, but as it’s a special occasion, I prefer the thicker double cream in the Saveur and Cook’s Illustrated recipes. Saveur and Southern Living also beat in eggs. I’m sceptical; as with the milk, I feel the less water in this casserole the better, but the eggs do give the filling a rich, almost custardy texture. To be safe, I decide to use just the yolks – you could even use the whites for a meringue topping if you’re feeling adventurous, but I’d save them for a puritan post-Thanksgiving breakfast.

The flavourings

Attempt to put a sugar-free sweet potato casserole on the table on Thanksgiving of all days, and you might just have your green card revoked; absolutely everyone adds some. But you don’t have to pour in a whole cup of the stuff, like Southern Living – it’s quite acceptable to stick with a more modest teaspoon, as Cook’s Illustrated suggests, just to accentuate the tuber’s natural sweetness. That said, I’m not going to stop you if you want to go mad on thankfulness for sugar once a year.

The Joy of Cooking’s sweet potato. Photograph: Felicity Cloake/Guardian

Chow and Saveur use dark brown sugar, Joy goes for the simple brown stuff, and no one else specifies, so I use white. As with the pumpkin pie, the more caramelised flavours of the less refined sugars are lovely in combination with the vegetable star, making it taste far more festive, and interesting, than ordinary caster.
Holiday or not, I draw the line at too many spices; the nutmeg, vanilla and cinnamon in the Saveur pie completely overwhelm the poor old potato. The warmth of its grated ginger is inspired, however – much fresher than Joy’s powdered variety or Chow’s crystallised version. That, and a sprinkling of nutmeg, is quite enough for me, though I’d also accept the merest pinch of cinnamon, given the American fondness for the stuff. Joy is the only recipe to balance the sugar with lemon juice – it works because of the ridiculous amount of sugar it uses, but my more restrained recipe renders such an addition unnecessary.

Southern Living’s sweet potato casserole. Photograph: Felicity Cloake/Guardian

Toppings

I have to admit, marshmallows aren’t really my thing outside a Wagon Wheel, but I do like the crunch of the various other toppings the recipes use. Joy goes for a simple brown sugar glaze while Saveur makes an oat and brown sugar crumble with chopped pecan nuts, which, though delicious, I find a bit heavy for a side dish. Southern Living’s crushed cornflakes go down surprisingly well, but in the end, I settle for a classic pecan praline, on the basis that, as I’ve reined back the sugar in the dish itself, I can afford a little on top.
It is Thanksgiving, after all. Whether you crown it with a whole heap of pink and white marshmallows is up to you.
(serves 4-6)
900g sweet potatoes
45g butter
1 egg yolk
2 tbsp double cream
1 tsp dark muscovado sugar
1 tsp grated ginger
Sprinkling of nutmeg
½ tsp salt
For the topping
15g dark muscovado sugar
2 tbsp flour
1 tbsp butter, melted
40g pecans, roughly chopped
Heat the oven to 220C/gas mark 7 and prick the sweet potatoes with a fork. Bake until soft – how long this takes will depend on the size of your sweet potatoes, but check after 45 minutes.
Turn the oven down to 180C/gas mark 4. When the potatoes are cool enough to handle, peel off the skins and put the flesh into a bowl and mash until smooth – or use a stick blender. Add the butter and beat in until melted, then beat in the remaining ingredients. Taste for seasoning.
Spoon into an oven dish. Mix together all the topping ingredients with a pinch of salt and sprinkle over the top of the potatoes. Bake for about 25 minutes until the topping is crunchy and brown.
Candied sweet potatoes – the king of the Thanksgiving table, or a sugary distraction from good honest mash? Are you a marshmallow fan, or does the very idea of serving them with gravy turn your stomach? And, for those celebrating Thanksgiving, what else will you be serving up?