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For a ‘Proper Proper Proper’ Baked Sweet Potato, Freeze It First

Try Junzi lead chef Lucas Sin’s method for recreating a favorite Chinese street food at home

An overhead photo shows a purple baked sweet potato sliced lengthwise, sitting on a brown cutting board. Lucas Sin

Lucas Sin held a small purple sweet potato in each hand, his phone balanced on the kitchen counter recording. November in New York meant the chill was setting in, and Sin took to Instagram to share his memory of the winters he spent in China as a kid, along with a recipe for what he dubbed — in all caps — “proper proper proper sweet potatoes!!”

“It’s cold, it’s wintery,” he said, painting the picture for his 43,000 Instagram followers. “You’re walking down the street and you see a woman with a shovel and this gigantic wok filled with rocks or pebbles or coals, and she’s digging in there, just flipping potatoes and rotating, and you get this beautiful waft… it’s the perfect snack.” Sin explained the unique conditions that make those wok-roasted sweet potatoes so magical: The freezing they go through when left outside in China’s coldest regions improves the texture of the potato’s flesh, while cooking at such a high heat results in smoky, caramelized outer edges.

As a kid in Hong Kong — where it never got quite cold enough for sweet potatoes to actually freeze — Sin still ate a version of this snack. He’d walk the streets with his nose up until he found a vendor engulfed in a cloud of sweet steam. A cook, standing at a small cart, would pass the warm potatoes over a low counter. “During a certain time of the year, all around Hong Kong, if you’re lucky, you’ll smell this a block or two away. The sweet potato is nice and charred outside, super, super fluffy inside,” says Sin, who now lives in New York. “They serve the sweet potato inside a brown paper bag, and you walk along the street eating it.”

Sin is the lead chef at Junzi, a fast-casual Chinese restaurant with locations throughout New York City. When the pandemic hit, and with would-be diners and beginner home cooks around the country stuck at home, Sin drew a wider Instagram audience with the approachable Chinese recipes he shared to his page. When Sin posts a cooking tip or recipe, it’s not long before it seems all his followers are in their own kitchens, posting recreations of his tomato egg drop noodle soup or steamed eggs dotted with XO sauce and scallions.

Recreating this gooey, sugar-oozing sweet potato is simple, and from his home kitchen, Sin shared the process to Instagram: Scrub a few small sweet potatoes of any variety, and put them into the freezer for an hour or two. Then, roast them on parchment paper or aluminum foil at 450 degrees. After an hour or so, once caramelized sugar is seeping from the potatoes and trapped steam has separated the skin from the flesh, they’re finished. But as the chef points out, it’s near impossible to overcook a sweet potato, the sugars becoming more concentrated as they cook.

“One of the core tenets of Chinese cooking is that water is flavorless,” Sin tells me. “So a lot of Chinese technique is to force the water out of something so that what’s left behind is the more concentrated essence of that ingredient. [By freezing the potatoes first,] the inside of the sweet potato becomes ice. As these crystals form, they start to break up the cell walls within, without puncturing the skin.” Sin describes this process as essentially macerating the uncooked flesh, so that once it bakes, it takes on a smooth mashed potato-like texture. “It’s important that the skin isn’t punctured. All that stuff is stuck inside of the sweet potato.”

Holding it up to the camera in the original video, Sin cut into a baked sweet potato to show off its fluffy insides. Cooks at home were quick to follow his lead, moving ice cubes aside to fit sweet potatoes in their freezers. One commenter wrote that the sweet potato she’d baked using the method “tastes like winter in China.” Another said it brought back memories of their own time there.

A split-screen GIF shows chef Lucas Sin from two angles, as he peels a baked purple sweet potato.
Sin shows off a sweet potato, fresh out of the oven.
Lucas Sin

“Instagram is a ridiculous place,” Sin says, laughing at the outsized response to his one-ingredient recipe. “My job is not content creation. I just tell people about Chinese food because I think people should know about it. Now, everyone and their mother are making this sweet potato.” Celebrities DM’d Sin, wanting more details on how to top their sweet potatoes, or asking if they should puncture the potatoes before baking. “What I love about the things that I have put up on Instagram is that they’re simultaneously so silly and so straightforward,” he says.

Sin topped his own sweet potato with whipped creme fraiche, spiced honey, toasted oats, and, as he put it “literally whatever is tasty and textured.” I sprinkled mine with homemade granola, and ate it at 3 p.m., still in my pajamas. On Instagram, others finished theirs off with sunflower butter, with dark and sticky date syrup, or just split them open and sprinkled them with salt.

Maybe going absolutely bonkers over a baked sweet potato does feel a little silly. But this snack, main course, dessert — however you treat it — is a fitting symbol for our shared emotional state as home cooks in the umpteenth month of this pandemic. We need something to feel special, to break us free of the monotony of cooking the same dishes with the same ingredients day, after day, after day. But still, for those of us privileged enough to be sequestered at home where we eat, work, and sleep, trips to the grocery store are infrequent. And unless you’re already somewhere where sweet potato vendors roam the streets, it’s going to be quite some time until boarding a flight and finding this treat, wrapped in a paper bag, is a safe option.

It’s reassuring to know that, though you’ve run out of flour and you’re low on eggs, that sprouting sweet potato in your cupboard can become something remarkable. You could follow in Sin’s footsteps and adorn it with spiced honey and black sugar. Or, he suggests, “just serve it as-is. It’s delicious.”