Peel and wash 1lb of sweet potatoes. Cut them into bite-sized pieces, about 1” squares.
Soak the cut sweet potatoes in water for 15-20 minutes. Dry them well with a paper towel.
Put sweet potatoes into a large bowl and toss with some vegetable oil until lightly but well-coated. Set air fryer to 400 degrees and fry for 10 minutes. Toss and fry for another 10 minutes, until browned and slightly crispy.
Pour sweet potatoes onto a plate lined with paper towels to absorb and oil.
While potatoes are cooking for the second 10 minutes, make the sauce. In a heated pan, put ⅓ cup of water and ⅓ cup of sugar. Cook it on medium heat without stirring for about 4-5 min or until the sugar is completely melted and the sauce is reduced a bit. Add 1 tablespoon vegetable oil, 1 tablespoon of mulyeot (if using), ¼ teaspoon of soy sauce and cook for another 3-5 min.
Reduce heat to low. Add the deep-fried sweet potatoes and mix them quickly. Sprinkle 2 teaspoons of sesame seeds.
Place the candied sweet potatoes on a plate. To prevent the sweet potatoes from sticking to the plate, coat the serving plate with vegetable oil. Enjoy!