Heat oven to 300°F. Scrub sweet potatoes and poke all over with a fork. Place in a roasting pan large enough to hold all the potatoes with a few inches in-between (I used a 12 x 16-inch roasting pan).
Cover with foil and bake until potatoes are easily pierced with a knife, but not mushy, about 60-70 minutes. Unwrap and let cool slightly. Raise oven temp to 450°F and arrange a rack to the top of the oven.
Meanwhile, combine serranos, coconut oil, lime zest and juice, sugar, and salt in a small saucepan. Cook over medium heat until the oil is melted and the sugar is dissolved, about 5 minutes.
Smash potatoes with the palm of your hand. Pour syrup over the top and roast in the top of the oven until blistered and browned, about 20-25 minutes. If you'd still like them a bit more brown you can stick them under the broiler for a few minutes more.
Sprinkle with chives and sea salt and serve.
