6 1/4 cups vegetable oil
2 medium sweet potatoes (about 1 1/4 pound)
1 cup sugar
Heat 6 cups of the vegetable oil in a 5-quart Dutch oven or medium two-handled pot until a deep-fry thermometer measures 300°F.
Meanwhile, peel the sweet potatoes and cut into bite-size pieces (about 1-inch; see Cook’s Note). Fry until tender, 8 to 10 minutes, reserving the oil. (Test by poking a sweet potato with a toothpick; if there is no resistance, it is ready.) Transfer to a paper towel-lined plate to drain.
Heat the oil to 350°F and fry the potatoes again until crispy, about 2 minutes. Transfer to the same paper towel-lined plate. Sprinkle with a pinch of kosher salt.
Stir together the sugar and remaining 1/4 cup vegetable oil in a large skillet until the sugar is slightly moistened. Cook over medium-high heat until amber in color, 5 to 6 minutes. The caramel and oil will look separated, which is okay.
Turn off the heat, add the fried sweet potatoes to the skillet and carefully toss until coated well. Carefully transfer to a serving plate. Dip a metal spoon or wooden chopstick into the hot caramel and quickly shake it over the potatoes to create long decorative strings of sugar over the potatoes. Repeat as desired. Enjoy the dish while hot.
** To cut the sweet potatoes with the maximum surface for the caramel to stick to: slice it in half lengthwise, cut a 1-inch piece on the diagonal, then rotate the potato about 90 degrees and cut another 1-inch piece on the diagonal. Repeat until there’s no more to cut.