In April 2008, Youngsun Lee opened Persimmon, a 24-seat East Village restaurant that specializes in neo-Korean cooking. Lee defines his style of cooking as being "not really fusion or new Korean," but rather a cuisine that is very traditional but uses only local ingredients, including some that are not available in Korea. "It's as if I came in the 1960s and had to cook Korean food," he explains. This means that butter will find its way, even if very lightly, in some dishes. Lee specializes in kimchi, he says, which change constantly based on ingredients available. Other than a kimchi stew and miso soup, which are available year-round, the prix fixe menu completely changes every two weeks. Lee shops mostly at farmers' markets, and at Korean markets for ingredients like fresh bamboo shoots. It took him about two years to find the ideal location for Persimmon, which has an open kitchen that allows him to interact with customers. He would have like the restaurant to be even smaller, but his investors—also known to him as mom and dad—felt differently.

Lee, who is of Korean origin, grew up in Flushing. He was always interested in food, he says, and started cooking while in junior high school, helping his mom make kimchi. He was also interested in art, however, and graduated from the School of Visual Arts with a degree in graphic design and fine arts. He worked in graphic design for three years, but really wanted to open a restaurant the whole time. Realizing he needed solid foundations before taking on such venture, he enrolled at ICE. He externed at Annisa, and then worked at En Japanese, followed by Craftbar for a total of two and a half years. From there he joined David Chang's enterprise with a position at Momofuku Noodle Bar, where he often made special kimchi and developed dishes with one of the sous chefs he knew from Craftbar. Each one of his positions taught him invaluable skills, from running the kitchen to running a whole restaurant.

While it is not always compatible with running a restaurant, Lee is an avid outdoorsman. He used to snowboard and bike a lot, and honeymooned in Alaska.